Phase angle measurement techniques in electrosurgical systems

ABSTRACT

Apparatus and associated methods relate to controlling electrical power of an electrotherapeutic signal that is provided to a biological tissue engaged by an electrosurgical instrument during a medical procedure. Electrical power—a product of a voltage difference across and an electrical current conducted by the engaged biological tissue—is controlled according to a therapeutic schedule. The electrotherapeutic schedule can be reduced or terminated in response to a termination criterion being met. In some examples, the termination criterion is a current characteristic, such as, for example, a decrease in current conducted by the engaged biological tissue. In some examples, the termination criterion is a biological tissue resistance characteristic, such as, for example, an increase in the biological tissue resistance that exceeds a predetermined delta resistance value.

CLAIM OF PRIORITY

This application is a Continuation of International Patent ApplicationSerial No. PCT/US2020/031857, titled “ELECTROSURGICAL SYSTEMS ANDMETHODS” to Kester J. Batchelor et al. and filed on May 7, 2020, whichis related to (1) U.S. Provisional Application No. 62/845,647, titled“ELECTROSURGICALLY SEALING BIOLOGICAL TISSUE BY CONTROLLING POWERPROVIDED THERETO” to Kester J. Batchelor et al. and filed on May 9,2019, and to (2) U.S. Provisional Application No. 62/905,318 titled“ELECTROSURGICALLY SEALING BIOLOGICAL TISSUE BY CONTROLLING POWERPROVIDED THERETO” to Kester J. Batchelor et al. and filed on Sep. 24,2019, and to (3) U.S. Provisional Application No. 62/905,366 titled“CORRECTING TISSUE RESISTANCE MEASUREMENTS USING TEMPORAL DATA” toHuisun Wang et al. and filed on Sep. 24, 2019, and to (4) U.S.Provisional Application No. 62/905,337 titled “PREDICTIVE PHASE CONTROLOF AN ELECTROTHERAPEUTIC PROCEDURE” to Huisun Wang et al. and filed onSep. 24, 2019, and to (5) U.S. Provisional Application No. 62/905,345titled “PULSED ELECTRICAL POWER PROVIDED TO SEALED TISSUE TO REDUCETISSUE STICKING” to Huisun Wang et al. and filed on Sep. 24, 2019, andto (6) U.S. Provisional Application No. 62/905,360 titled “IMPEDANCEPHASE DETECTION FOR SHORT CIRCUIT PREDICTION” to Wayne Williams et al.and filed on Sep. 24, 2019, the entire content of each beingincorporated herein by reference in its entirety, and the benefit ofpriority of each is claimed herein.

BACKGROUND

Electrosurgery is the application of an electrical signal—anelectrotherapeutic signal—to produce a change in biological tissue of asurgical patient in some manner. Various electrosurgical techniques areused to cut, coagulate, desiccate, or fulgurate the biological tissue.These electrosurgical techniques and others can be performed duringvarious medical procedures, such as, for example, laparoscopicsurgeries. These medical procedures include: appendectomy,cholecystectomy, colectomy, cystectomy, gastric banding, gastric bypass,hernia repair, nephrectomy, Nissen fundoplication, prostatectomy, sleevegastrectomy, and others. Each of these medical procedures can have oneor more electrotherapeutic phases, such as, for example, interrogationphase, heating phase, drying phase, cauterizing phase, etc.

The electrotherapeutic signals used in such medical procedures can begenerated by an electrosurgical generator and then provided to thebiological tissue via an electrosurgical instrument, which can beelectrically connected to the electrosurgical generator. Theelectrosurgical instrument can be configured to mechanically andelectrically engage the biological tissue to which theelectrotherapeutic signal is provided. Various types of suchelectrosurgical instruments can be employed, including, for example,various types of forceps, conductive spatulas, electrical pads, etc.

Different medical procedures can implement different electrotherapeuticsignals so as to achieve results specific to these different medicalprocedures. Various electrical metrics of the electrotherapeutic signalsprovided to the engaged biological tissue can be used to characterizethese electrotherapeutic signals. These electrical metrics include:polarity (monopolar, bipolar), AC and/or DC, frequency, signalamplitude, attack and decay profiles, etc. Electrosurgical generatorsthat generate these various electrotherapeutic signals can control oneor more of these electrical metrics so as to provide electrotherapeuticsignals that yield efficacious results in the biological tissue engagedby the electrosurgical instrument.

SUMMARY

Apparatus and associated methods relate to a system for providingcontrolled electrical power to biological tissue. The electrosurgicalsystem includes a forceps having opposable jaw members configured toopen and close. The forceps also has a handpiece having a gripping leverconfigured to cause the opposable jaw members to open and close. Theopposable jaw members, when closed, are configured to clamp thebiological tissue therebetween in a manner that provides electricalcommunication between the opposable jaw members via the clampedbiological tissue. The electrosurgical system also includes anelectrosurgical generator electrically couplable to the forceps. Theelectrosurgical generator includes an electrical-energy source inelectrical communication with the opposable jaw members when theelectrosurgical generator is electrically coupled to the forceps. Theelectrical-energy source is configured to generate electrotherapeuticsignals. The electrosurgical generator includes a control circuitconfigured to cause the electrical-energy source to provide anelectrotherapeutic signal to the clamped biological tissue during anelectrotherapeutic phase. Electrical power of the providedelectrotherapeutic signal is controlled according to anelectrotherapeutic schedule.

Some examples relate to an electrosurgical generator for providingcontrolled electrical power to biological tissue engaged by anelectrosurgical instrument. The electrosurgical generator includes anelectrical connector configured to electrically couple theelectrosurgical instrument to the electrosurgical generator so as toprovide electrical communication between the electrosurgical generatorand the engaged biological tissue. The electrosurgical generatorincludes an electrical-energy source electrically coupled to theelectrical connector and configured to generate an electrotherapeuticsignal. The electrosurgical generator also includes a control circuitconfigured to cause the electrical-energy source to provide theelectrotherapeutic signal to the engaged biological tissue during anelectrotherapeutic phase. Electrical power of the electrotherapeuticsignal is provided to the engaged biological tissue controlled accordingto an electrotherapeutic schedule.

Some examples relate to a method for providing controlled electricalpower to biological tissue engaged by an electrosurgical instrument. Themethod includes the step of engaging, via the electrosurgicalinstrument, the biological tissue in a manner that provides electricalcommunication between the electrosurgical instrument and the engagedbiological tissue. The method proceeds to the step of providing, via anelectrical-energy source in electrical communication with theelectrosurgical instrument, an electrotherapeutic signal to the engagedbiological tissue during an electrotherapeutic phase. The method alsoincludes the step of controlling electrical power of the providedelectrotherapeutic signal according to an electrotherapeutic schedule.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrosurgical system providingelectrotherapy to biological tissue of a surgical patient.

FIG. 2 is a block diagram of an electrosurgical system for sealingbiological tissue engaged by an electrosurgical instrument.

FIGS. 3A-3B are flow charts of a method for sealing a biological tissueengaged by an electrosurgical instrument.

FIG. 4 is a graph depicting examples of an electrical-power scheduleused to control electrical power provided to biological tissue beingsealed.

FIG. 5 is a flow diagram depicting an example of open circuit checktechniques that can be used in a surgical system.

FIG. 6 is a flow chart of a biological tissue-sealing method that usesan electrical-power schedule corresponding to a size of biologicaltissue engaged by the electrosurgical instrument.

FIG. 7A is a graph depicting measured tissue resistance as a function ofjaw temperature of a forceps.

FIG. 7B is a graph depicting jaw temperature vs. time after terminationof power application.

FIG. 8 is a graph depicting resistance compensation vs. time after powerapplication.

FIG. 9 depicts a flow chart a method for compensating measurements oftissue resistance as a function of time after power application.

FIGS. 10A-10D are graphs of electrical parameters of anelectrotherapeutic signal of an electrotherapy having a pulsed stickingreduction portion

FIG. 11 is a flow chart of a method for reducing sticking betweenbiological tissue and an electrosurgical instrument.

FIG. 12 is a graph depicting examples of impedance-angle/time relationsof biological tissues with and without metal objects therein.

FIG. 13 is a flow chart of a method for determining presence or absenceof a metal object in biological tissue engaged by an electrosurgicalinstrument.

FIG. 14 is a flow diagram depicting an example of a two-boundarytechnique that can be used in a surgical system.

FIG. 15 is a flow diagram depicting an example of open circuit checktechniques that can be used in a surgical system.

FIG. 16 is a flow diagram depicting another example of the open circuitcheck techniques that can be used in a surgical system.

FIG. 17 is a flow diagram depicting an example of power correctiontechniques that can be used in a surgical system.

FIG. 18 is a simplified block diagram of an example of a combinationultrasonic energy and electrosurgical energy system that can implementvarious techniques of this disclosure.

FIG. 19 is a flow diagram depicting an example of a reduced thermalmargin technique that can be used in a combination ultrasonic energy andelectrosurgical energy system.

FIG. 20 is a flow diagram depicting an example of a thermal margincontrol technique that can be used in an electrosurgical system.

FIG. 21 is a flow diagram depicting another example of a thermal margincontrol technique that can be used in an electrosurgical system.

FIGS. 22A-22D depict a flow diagram of an example of an energy deliverytechnique that can use, among other things, an amount of energydelivered to a biological tissue in its decision-making process.

FIG. 23 is graph depicting an example of a relationship between a changein the value of a measured electrical parameter to a change in power.

FIG. 24 is a flow diagram depicting another example of power correctiontechniques that can be used in a surgical system.

DETAILED DESCRIPTION

Apparatus and associated methods relate to application ofelectrotherapeutic signals to biological tissues engaged by anelectrosurgical instrument. Control of various electrical metrics ofthese electrotherapeutic signals will be disclosed below as will thespecific electrosurgical techniques that perform such control. Thisspecification is organized into sections titled: i) Electrical PowerControl of Electrotherapeutic Signals (FIGS. 1-4); ii) Predictive PhaseControl of an Electrotherapeutic Signal (FIGS. 5-6); iii) Correction ofMeasured Electrical Resistance of Engaged Biological Tissue (FIGS. 7A-7Band 9); iv) Modification of Initial Impedance (FIG. 9); v) ReducingSticking of Biological Tissue to Electrosurgical Instrument by PulsingElectrical Power of Electrotherapeutic Signal (FIGS. 10A-10D and 11);vi) Determining Presence or Absence of a Conductive Foreign Body inBiological Tissue Engaged by an Electrosurgical Instrument (FIGS. 12 and13); vii) Short Circuit Error Trapping with Band Between Trigger andEscape Values (FIG. 14); viii) Open Circuit Check for Impedance LimitEndpoint Waveform (FIGS. 15 and 16); ix) Alternate Power CorrectionOutputs in Low Accuracy Hardware Systems (FIG. 17); x) Reduced ThermalMargin Combination Energy Device (FIGS. 18 and 19); xi) Staged ImpedanceValues to Control Thermal Margins in Systems with Slow CPUs (FIGS. 20and 21); xii) Consumed Energy Monitoring and Open Circuit Evaluation(FIGS. 22A-22D); xiii) Dwell Time Between Pulses; and xiv) IncrementalAdjustment of Control Parameter as a Function of a Monitored Variable.The techniques are described in these separate sections for purposes ofexplanation only. Unless stated explicitly to the contrary, each ofthese techniques can be used in combination with one or more of theother techniques described in this disclosure.

Electrical Power Control of Electrotherapeutic Signals (FIGS. 1-4)

Electrosurgically sealing or coagulating biological tissue engaged by anelectrosurgical instrument is an electrosurgical technique used invarious medical procedures. The engaged biological tissue can beelectrosurgically sealed by heating the engaged biological tissue in acontrolled manner. In some medical procedures, the biological tissuethat is being sealed is a vessel. Heating of the vessel causes thecollagen found in the vessel walls to become denatured. This denaturedcollagen forms a gel-like substance acting as glue between the vesselwalls. When forced together and maintained together while cooling,opposite walls of a vessel will then form a seal.

Heating of the vessel is carefully controlled so that neither too littlenor too much energy is provided to the vessel. If too much energy isprovided thereto, then charring and/or burning of the vessel wall canoccur. If too little energy is provided thereto, then seal quality ofthe vessel can be poor. One measure of seal quality is a pressuredifference that the sealed vessel can withstand without bursting. Lowquality seals can be compromised when the pressure applied theretoexceeds some value.

The rate at which the energy is provided to the vessel can also becarefully controlled so as to facilitate rapid performance of theelectrosurgical procedure. Rapid performance of electrosurgicalprocedures reduces the time and difficulty of these procedures. The rateof heating, however, should not be so rapid as to cause uncontrolledboiling of fluid within the biological tissue. Uncontrolled boiling canrupture engaged or nearby biological tissues and/or compromise thequality of the seal.

Heating of the engaged biological tissue can be controlled bycontrolling the electrical power of an electrotherapeutic signalprovided to and dissipated by the engaged biological tissue. Suchelectrical power can be controlled according to a sealing schedule. Forexample, the sealing schedule can be indicative of a product of avoltage difference across and an electrical current conducted by theengaged biological tissue. Thus, the sealing schedule is anelectrical-power schedule. In some examples, the electrotherapeuticsignal can be reduced or terminated in response to a terminationcriterion being met. In some examples, the termination criterion is acurrent characteristic, such as, for example, a decrease in currentconducted by the engaged biological tissue. In some examples, thetermination criterion is a resistance characteristic, such as, forexample, an increase in the electrical resistance of the engagedbiological tissue. Such an increase in the electrical resistance inexcess of a predetermined delta resistance value can be used as atermination criterion, for example, where the predetermined deltaresistance value is the difference between the measured resistance (orimpedance) and the lowest value of the resistance (or impedance)measured in the pulse. In some examples, the termination criterion is atemporal condition, such as, for example, a time duration, predeterminedor calculated based on some condition.

Electrical impedance is complex and, as such, includes a real component(resistance) and an imaginary component (reactance). This documentdescribes techniques using impedance or resistance. It should beunderstood that where complex impedance values are available, suchvalues can be used in place of resistance values. Conversely, where nocomplex impedance values are available, resistance values can be usedinstead unless otherwise stated.

In addition, many of the techniques below describe deliveringelectrosurgical energy to biological tissue. Unless indicated to thecontrary, each of these techniques can deliver the electrosurgicalenergy using either power-controlled or voltage-controlled techniques.In a power-controlled implementation, a control circuit can controldelivery of electrosurgical energy using a product of the voltageapplied across the engaged biological tissue and the electrical current,e.g., according to a plan or schedule. For example, the control circuitcan control delivery of a constant power or a monotonically increasingpower during a particular phase, e.g., drying phase.

This document describes, among other things, one or more techniques forproviding electrotherapy, which can be provided according to a treatmentor other plan. The plan can include a recipe, prescription, regimen,methodology, or the like. The plan can include one or more temporalaspects, such as a schedule, such as can include occurrence orrecurrence (or inhibition or suppression) timing, frequency, type,relative combination (e.g., coagulation relative to cutting) or thelike. The plan can include electrotherapy waveform information, such ascan include pulse width, duty cycle, on duration, off duration,repetition rate, amplitude, phase, or the like The plan need not bestatic or a priori in nature, but can include one or more dynamicaspects, such as can be modified or governed, such as by diagnostic,operational, or other information obtained during or betweenelectrotherapy delivery instances, including in a closed-loop, or otherfeedback manner. One or more aspects of the plan can be tailored, suchas to the specific patient, to a sub-population of patients such as whoshare one or more specified characteristics, or a population ofpatients, such as can be based on stored patient data, or by user inputsuch as which may be provided by the patient or by a caregiver. The plancan include one or more conditional aspects, such as can include one ormore branch conditions, such as can be determined using a patientcharacteristic, a diagnostic measure, an efficacy determination, or anoperational characteristic of the device or its environment. Such branchconditions may be determined automatically, by the device, e.g., withoutrequiring user input, or may involve user input, such as can be providedbefore, during, or after one or more portions of operations of theelectrotherapy device according to the plan. The plan can involvecommunicating with or using another device, such as to receive orprovide one or any combination of inputs, outputs, or instructions,operating parameters, or measured data. One or more aspects of the plancan be recorded or encoded onto a medium, such as a computer or othermachine-readable medium, such as can be a tangible medium.

In a voltage-controlled implementation, the control circuit can controlthe voltage of the electrosurgical energy delivered, e.g., according toa plan, regimen, or schedule. For example, the control circuit cancontrol delivery of a constant voltage or a monotonically increasingvoltage during a particular phase, e.g., drying phase.

FIG. 1 is a perspective view of an electrosurgical system providingelectrotherapy to biological tissue of a surgical patient. In FIG. 1,electrosurgical system 10 includes electrosurgical generator 12 andforceps 14, which is shown engaging biological tissue 16.Electrosurgical generator 12 is generating an electrotherapeutic signalwhich is provided to engaged biological tissue 16 via forceps 14.Although FIG. 1 depicts forceps 14 engaging and delivering theelectrotherapeutic signal to biological tissue 14, various types ofelectrosurgical instruments, such as those disclosed above, can be usedfor such purposes.

Various types of forceps as well can be used for delivering theelectrotherapeutic signal to biological tissue 14. For example, forceps14 can be medical forceps, cutting forceps, or an electrosurgicalforceps (e.g., monopolar or bipolar forceps). Forceps 14, in someexamples, can be used for medically related procedures, such as openand/or laparoscopic medical procedures to manipulate, engage, grasp,cut, cauterize, seal, or otherwise affect a vessel, biological tissue,vein, artery, or other anatomical feature or object.

As illustrated in FIG. 1, forceps 14 includes hand piece 18, shaftassembly 20, knife blade assembly 22, and gripping assembly 24. In someexamples, such as the illustrated example of FIG. 1, forceps 14 iselectrically connected to electrosurgical generator 12, which generatesthe electrotherapeutic signal and provides the generatedelectrotherapeutic signal to forceps 14. Forceps 14 then electricallycommunicates the electrotherapeutic signal to gripping assembly 24and/or to a remote pad, which can be employed for variouselectrosurgical techniques, such as cauterizing, sealing, or other suchelectrosurgical techniques.

Hand piece 18 includes handle 26, gripping lever 28, knife trigger 30,electrical therapy actuation button 32, and rotation wheel 34. Grippingassembly 24 includes first jaw member 36 and second jaw member 38. Shaftassembly 20 is connected at a proximal end to hand piece 18, and at adistal end to gripping assembly 24. Shaft assembly 20 extends distallyfrom hand piece 18 in longitudinal direction 40 to gripping assembly 24.

Shaft assembly 20 functions to permit a portion of forceps 14 (e.g.,gripping assembly 24 and a distal portion of shaft assembly 20) to beinserted into a patient or other anatomy while a remaining portion offorceps 14 (e.g., hand piece 18 and a remaining proximal portion ofshaft assembly 20) are outside of the patient or other anatomy. Thoughillustrated in FIG. 1 as substantially straight, in other examples,shaft assembly 20 can include one or more angles, bends, and/or arcs.Shaft assembly 20 can be a cylinder with a circular, elliptical, orother cross-sectional profile, or other elongated member that extendsfrom hand piece 18 to gripping assembly 24. In some examples, the shaftcan be bendable, steerable or otherwise deflectable.

In some examples, such as the example of FIG. 1, shaft assembly 20 caninclude an elongated hollow member (e.g., a tubular outer shaft) thatencloses knife blade assembly 22 and mechanical linkage to couple knifeblade assembly 22 with knife trigger 30. In general, shaft assembly canbe any elongated member having stiffness sufficient to transfer forcesalong longitudinal direction 40. Shaft assembly 20 also can includeconductive elements (e.g., wires, a conductive outer shaft and/or aconductive inner shaft, etc.) to provide electrical communicationbetween hand piece 18 and gripping assembly 24, so as to communicate anelectrotherapeutic signal thereby.

Gripping lever 28, knife trigger 30, electrical therapy actuation button32, and rotation wheel 34 of hand piece 18, each are configured to causevarious actuations, usually at the distal end, of shaft assembly 20. Forexample, actuation of gripping lever 28 is configured to controloperation of gripping assembly 24 at the distal end of shaft assembly20. Gripping lever 28 is a gripping actuator that is movable between anopen configuration position (illustrated in FIG. 1) and a closedconfiguration position in which gripping lever 28 is moved proximallytoward handle 26. Movement of gripping lever 28 proximally toward handle26 to the closed configuration position causes gripping assembly 24 totransition from the open configuration to the closed configuration.Movement of gripping lever 28 distally (e.g., release of gripping lever28 to the open configuration position causes gripping assembly 24 totransition from the closed configuration to the open configuration.

Such transitions between the open and closed configurations of grippingassembly 24 are realized by one or more of first and second jaw members36 and 38 moving between an open configuration (illustrated in FIG. 1),in which first and second jaw members 36 and 38 are spaced apart, and aclosed configuration, in which the gap between first and second jawmembers 36 and 38 is reduced or eliminated. Various electrosurgicalinstruments engage biological tissue 16 in various manners. In someelectrosurgical instruments, such as the one illustrated in FIG. 1,first and second jaw members 36 and 38 are opposable to one another. Inthe depicted example first and second jaw members 36 and 38 areconfigured to clamp biological tissue 16 therebetween in a manner thatprovides electrical communication between opposable jaw members 36 and38 via clamped biological tissue 16. Other electrosurgical instrumentscan engage biological tissue in other manners.

Mechanical linkage within shaft assembly 20 can be configured to causeone or more of first and second jaw members 36 and 38 to move betweenthe open configuration and the closed configuration in response toactuation of gripping lever 28. One example mechanism for causingmovement of a gripping assembly between the open and closedconfigurations can be found in U. S. Patent Publication No.2017/0196579, entitled “FORCEPS JAW MECHANISM” and filed on Jan. 10,2017 to Batchelor et al., the contents of which are hereby incorporatedby reference in their entirety.

Actuation of knife trigger 30 is configured to control operation ofknife blade assembly 22 located at the distal end of shaft assembly 20.Knife blade assembly 22 is configured to cut, excise, or otherwiseaffect biological tissue or other object(s) clamped between first andsecond jaw members 36 and 38. Knife trigger 30 is a knife blade actuatorthat is movable between a retracted configuration position (illustratedin FIG. 1) and a deployed or extended configuration position in whichknife trigger 30 is moved proximally toward handle 26 to cause knifeblade assembly 22 to cut biological tissue 16, which is clamped betweenfirst and second jaw members 36 and 38. Movement of knife trigger 30proximally toward handle 26 to the deployed configuration positioncauses a cutting blade of knife blade assembly 22 to engage biologicaltissue 16, thereby cutting biological tissue 16. Movement of knifetrigger 30 distally (e.g., release of knife trigger 30) causes the knifeblade to retract from clamped biological tissue 16. Mechanical linkage,for example, within shaft assembly 20 can be configured to cause theknife blade to engage and retract from engaged biological tissue 16.

Rotation wheel 34 is configured to control rotational configuration ofone or more of knife blade assembly 22, and gripping assembly 24 at thedistal end of shaft assembly 20 and/or control rotational configurationof shaft assembly 20. Movement (e.g., rotation) of rotation wheel 34causes rotation of one or more of shaft assembly 20, knife bladeassembly 22, and gripping assembly 24 about an axis extending inlongitudinal direction 40. Such rotational control can facilitatealignment of gripping assembly and/or knife blade assembly with clampedbiological tissue 16.

Therapy actuation button 32 is configured to control generation and/ordelivery of the electrotherapeutic signal to engaged biological tissue16. Actuation of therapy actuation button 32 causes anelectrotherapeutic signal, drawn from e.g., electrosurgical generator12, to be applied to one or more of first and second jaw member 36 and38, a remote pad (not illustrated), or other portions of forceps 14 tocauterize, seal, or otherwise electrically affect a patient or otheranatomy. One example of a hand piece utilizing a gripping lever, knifetrigger, rotation wheel, and therapy actuation button can be found inU.S. Pat. No. 9,681,883, entitled “FORCEPS WITH A ROTATION ASSEMBLY” andissued on Jun. 20, 2017 to Windgassen et al., the contents of which arehereby incorporated by reference in their entirety.

FIG. 2 is a block diagram of an electrosurgical system for sealingbiological tissue engaged by an electrosurgical instrument. In FIG. 2,electrosurgical system 10 include electrosurgical generator 12 andelectrosurgical instrument 14′. Electrosurgical instrument 14′ can beany electrosurgical instrument configured to engage and deliver anelectrotherapeutic signal to biological tissue. Electrosurgicalgenerator 12 is configured to generate the electrotherapeutic signal,such as a high frequency (AC) electrical signal, that electrosurgicalinstrument 14′ delivers to engaged biological tissue 16.

In some examples, electrosurgical instrument 14′ is a forceps having ahandpiece coupled to opposable jaw members via a shaft assembly, such asforceps 14 depicted in FIG. 1. In other examples, electrosurgicalinstrument 14′ is a conductive spatula, a conductive pad, or otherelectrosurgical device. These various types of electrosurgicalinstruments have various ways of engaging biological tissues (e.g.,clamping, touching, surrounding, penetrating, radiating, etc.)

Electrosurgical generator 12 includes instrument interface 42,electrical-energy source 44, measurement circuit 46, control circuit 48,and user interface 50. Instrument interface 42 can include signaldrivers, buffers, amplifiers, ESD protection devices, and electricalconnector 52, for example. Electrical connector 52 is configured toelectrically couple electrosurgical instrument 14′ to electrosurgicalgenerator 12 so as to provide electrical communication betweenelectrosurgical generator 12 and electrosurgical instrument 14′. Suchelectrical communication can be used to transmit operating power and/orelectrical signals therebetween. Electrosurgical instrument 14′, inturn, can provide electrical communication between electrical connector52 and biological tissue engaged thereby.

Electrical-energy source 44 is configured to generate anelectrotherapeutic signal to be delivered to the engaged biologicaltissue via electrically connected electrosurgical instrument 14′. Thegenerated electrotherapeutic signal can be controlled so as to obtainthe desired result for a specific electrosurgical procedure. In oneexample, for example, the electrotherapeutic signal is configured toresistively heat the engaged biological tissue so as to surgicallyaffect, such as seal, the engaged biological tissue. Such controlling ofthe electrotherapeutic signal will be further disclosed below.

Measurement circuit 46 is configured to measure one or more electricalparameters of biological tissue engaged by connected electrosurgicalinstrument 14′. Measurement circuit 46 is in electrical communicationwith connected electrosurgical instrument 14′ when electrosurgicalgenerator 12 is electrically connected to electrosurgical instrument 14′via electrical connector 52. Various examples of measurement circuit 46are configured to measure various electrical parameters. For example,measurement circuit 46 can be configured to measure voltage differencedelivered across and/or electrical current conducted by the engagedbiological tissue. In some examples, measurement circuit 46 can beconfigured to measure phase angle between voltage difference deliveredacross and electrical current conducted by the engaged biologicaltissue. In some examples, measurement circuit 46 is configured tomeasure DC and or AC electrical parameters of the engaged biologicaltissue.

Measured parameters, such as voltage difference delivered across and/orelectrical current conducted by the engaged biological tissue can beused to determine other electrical metrics. For example, measurements ofvoltage difference delivered across and/or electrical current conductedby the engaged biological tissue can be used to determine electricalresistance of the engaged biological tissue. Measurements of voltagedifference delivered across and electrical current conducted by theengaged biological tissue, as well as the phase angle therebetween canbe used to determine complex impedance of the engaged biological tissue.Measurements of voltage difference delivered across and electricalcurrent conducted by the engaged biological tissue, as well as the phaseangle therebetween also can be used to determine apparent power (VA)and/or real power (W) provide to the engaged biological tissue.

Such measurements of electrical parameters can be used for controllingan electrotherapeutic signal during delivery to an engaged biologicaltissue. For example, measurements of the voltage difference deliveredacross and measurements of the electrical current conducted by theengaged biological tissue can be used to determine and/or control thereal power provided to the engaged tissue. This determined real powercan then be compared with an electrotherapeutic schedule. Such acomparison could be used to generate an error signal. Measurements ofelectrical parameters can also be used to determine phase-controlcriteria for controlling phases of electrotherapy. Phase-controlcriteria can include criteria for commencement and termination of aphase, as well as criteria for intra-phase control.

Control circuit 48 is configured to control operation ofelectrical-energy source 44 and/or measurement circuit 46. Controlcircuit 48 is electrically connected to electrical-energy source 44 andmeasurement circuit 46. Control circuit 48 causes electrical-energysource to provide an electrotherapeutic signal to biological tissueengaged by electrically connected electrosurgical instrument 14′.Control circuit 48 causes electrical-energy source 44 to generate theelectrotherapeutic signal according to an electrotherapeutic schedulesuch that the generated electrotherapeutic signal is controlled for aspecific electrosurgical procedure.

Various electrotherapeutic schedules can be used to effectuate varioustypes of electrotherapy. For example, in some examples, real power (W)of the electrotherapeutic signal provided to the engaged biologicaltissue is controlled according to an electrical-power schedule. In otherexamples, voltage difference (V) of the electrotherapeutic signaldelivered across the engaged biological tissue is controlled accordingto a voltage schedule. In other examples, electrical current (A) of theelectrotherapeutic signal conducted by the engaged biological tissue iscontrolled according to an electrical-current schedule. In still otherexamples, apparent power (VA) of the electrotherapeutic signal providedto the engaged biological tissue can be controlled according to avoltage-amperage schedule.

Control circuit 48, for example, can cause electrical-energy source 44to provide energy to engaged biological tissue, such that a product of avoltage difference across and an electrical current conducted by theengaged biological tissue is controlled according to theelectrotherapeutic schedule. Control circuit 48 can use the comparisonof the determined real power with an electrotherapeutic schedule togenerate an error signal. Such an error signal can be used in aclosed-loop feedback system that includes electrical-energy source 44,so as to generate the electrotherapeutic signal according to theelectrotherapeutic schedule.

As illustrated in FIG. 2, control circuit 48 includes processor 54 andmemory 56. Control circuit 48 can include a timer and/or a clock. Insome examples, the timer and/or the clock are part of processor 54. Inother examples, the timer and/or clock are separate from the processor54. Processor 54, in one example, is configured to implementfunctionality and/or process instructions for execution withinelectrosurgical system 10. For instance, processor 54 can be capable ofreceiving from and/or processing instructions stored in program memory56P. Processor 54 can then execute program instructions so as to causeelectrical-energy source 44 to generate the electrotherapeutic signalaccording to a predetermined electrotherapeutic schedule. Thepredetermined electrotherapeutic schedule can be retrieved from datamemory 56D, for example. Processor 54 can compare electrical parametersmeasured by measurement circuit 46 with the retrieved predeterminedelectrotherapeutic schedule. Processor 54 can send commands toelectrical-energy source 44 and/or measurement circuit 46. Processor 54also can also send or receive information from user interface 50.

In various examples, electrosurgical generator 12 can be realized usingthe elements illustrated in FIG. 2 or various other elements. Forexample, processor 54 can include any one or more of a microprocessor, acontrol circuit, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field-programmable gate array(FPGA), or other equivalent discrete or integrated logic circuitry.

Memory 56 can be configured to store information within electrosurgicalsystem 10 during operation. Memory 56, in some examples, is described ascomputer-readable storage media. In some examples, a computer-readablestorage media can include a non-transitory medium. The term“non-transitory” can indicate that the storage medium is not embodied ina carrier wave or a propagated signal. In certain examples, anon-transitory storage medium can store data that can, over time, change(e.g., in RAM or cache). In some examples, memory 56 is a temporarymemory, meaning that a primary purpose of memory 56 is not long-termstorage. Memory 56, in some examples, is described as volatile memory,meaning that memory 56 does not maintain stored contents when power toelectrosurgical system 10 is turned off. Examples of volatile memoriescan include random access memories (RAM), dynamic random access memories(DRAM), static random access memories (SRAM), and other forms ofvolatile memories. In some examples, memory 56 is used to store programinstructions for execution by processor 54. Memory 56, in one example,is used by software or applications running on electrosurgical system 10(e.g., a software program implementing electrical control of anelectrotherapeutic signal provide to biological tissue engaged by anelectrosurgical instrument) to temporarily store information duringprogram execution, such as, for example, in data memory 56D.

In some examples, memory 56 can also include one or morecomputer-readable storage media. Memory 56 can be configured to storelarger amounts of information than volatile memory. Memory 56 canfurther be configured for long-term storage of information. In someexamples, memory 56 includes non-volatile storage elements. Examples ofsuch non-volatile storage elements can include magnetic hard discs,optical discs, flash memories, or forms of electrically programmablememories (EPROM) or electrically erasable and programmable (EEPROM)memories.

User interface 50 can be used to communicate information betweenelectrosurgical system 10 and a user (e.g., a surgeon or technician).User interface 50 can include a communications module. User interface 50can include various user input and output devices. For example, Userinterface can include various displays, audible signal generators, aswell switches, buttons, touch screens, mice, keyboards, etc.

User interface 50, in one example, utilizes the communications module tocommunicate with external devices via one or more networks, such as oneor more wireless or wired networks or both. The communications modulecan include a network interface card, such as an Ethernet card, anoptical transceiver, a radio frequency transceiver, or any other type ofdevice that can send and receive information. Other examples of suchnetwork interfaces can include Bluetooth, 3G, 4G, and Wi-Fi radiocomputing devices as well as Universal Serial Bus (USB) devices.

FIGS. 3A-3B are flow diagrams of a non-limiting example of a method forgenerating an electrotherapeutic signal for sealing a biological tissueengaged by an electrosurgical instrument. Method 100 illustrated inFIGS. 3A-3B can be used with an electrosurgical system such aselectrosurgical system 10 depicted in FIGS. 1-2. Using varioustechniques described below, an electrosurgical generator can control anenergy delivery of the therapeutic signal provided to the biologicaltissue during a portion of a therapeutic phase according to anincremental change in energy delivery as a function of a change in ameasured electrical parameter of the biological tissue. In someexamples, a control circuit can control the electrical power of thetherapeutic signal provided to the biological tissue during a portion ofa therapeutic phase according a therapeutic plan, such as by controllingthe power during the phase that provides the tissue modification.

For example, a control circuit can incrementally modify the power as afunction of current. In some examples, the function of current is afunction of a change in current. The change in current can be the changein the current over the course of a pulse and, as such, can look morelike a current value. In some examples, the function of current is afunction of an instantaneous measured change in current and, as such,can look more like the slope of the current function. The controlcircuit can modify the power based upon either of these—current orinstantaneous change in current. In some examples, the function of theinstantaneous measured change in current is a linear function. In otherexamples, the control circuit can incrementally modify the power as afunction of resistance, such as when using a voltage-controlledtechnique.

As seen in FIG. 4, in some examples, the system can control theelectrical power of the therapeutic signal provided to the biologicaltissue during a portion of the therapeutic phase using a pre-definedpower curve. In some examples, the pre-defined power curve can includetwo or more linear portions.

It should be noted that the FIGS. 3A and 3B and FIG. 4 are non-limitingspecific examples used for purposes of explanation.

In some examples, the method can switch from using a power-controlledtechnique to using a voltage-controlled technique. In avoltage-controlled technique, current can be capped but allowed to movefreely according to the responding impedance, which can allow for avariable power delivery. For example, the control circuit can deliver apulse using power-controlled techniques and as the resistance increases,approaches a boiling condition, or reaches a threshold, the system canswitch to a voltage-controlled technique. In this manner, at thebeginning the system can take advantage of power-controlled techniquesto deliver energy faster, but closer to boiling the system can switchover to voltage-controlled techniques, which can be more responsive. Insome implementations that use a voltage-controlled technique, the systemcan control the electrical power of the therapeutic signal provided tothe biological tissue during a portion of the therapeutic phase using apre-defined voltage curve. In some examples, the pre-defined voltagecurve can include two or more linear portions.

In FIG. 3A, method 100 begins at step 102, in which the electrosurgicalsystem 10 (depicted in FIGS. 1-2) is powered on. Then, at step 104, aninterrogation phase begins, in which control circuit 48 (depicted inFIG. 2) causes electrical-energy source 44 (depicted in FIG. 2) toprovide an interrogation signal, such as an interrogation pulse, to theengaged biological tissue during the interrogation phase. Power (W) ofthe provided interrogation signal is controlled according to aninterrogation schedule. In some examples, the power levels provided tothe engaged biological tissue during the interrogation phase can be lowso as to cause little or no tissue effect. Such low power levels can beprovided for the purpose of obtaining measurements of electricalproperties of the engaged biological tissue. Such measurements aresometimes obtained before electrotherapy is provided so as to obtain apre-electrotherapy measurement. In some examples, the interrogationschedule is indicative of providing constant electrical power during theinterrogation phase. Such a schedule can be called a constant powerschedule. In some examples, control circuit 48 terminates theinterrogation phase after a predetermined time duration.

At step 106, controller 48 causes measurement circuit 46 (depicted inFIG. 2) to measure a first electrical resistance of the engagedbiological tissue during an interrogation phase. The first time thatstep 106 is performed this measured electrical resistance is a referenceresistance. Then, at step 108, control circuit 48 compares the measuredelectrical resistance with a minimum resistance previously measured (ifany). If, at step 108, the measured electrical resistance is lower thanthe minimum resistance, then the method advances to step 110, where themeasured electrical resistance is recorded as the new minimum value, andthen the method advances to step 116 (where a first interval of thedrying or desiccation phase begins). If, however, at step 108, themeasured electrical resistance is greater than the minimum resistance,then the method advances to step 112, where control circuit 48 comparesthe measured electrical resistance with a sum of the minimum resistanceand a predetermined resistance delta. If, at step 112, the measuredelectrical resistance is less than the sum of the minimum resistance anda predetermined resistance delta, then the method advances to step 114,where the measured electrical resistance is disregarded. If, however, atstep 112, the measured electrical resistance is greater than the sum ofthe minimum resistance and a predetermined resistance delta, then themethod advances to step 146 illustrated in FIG. 3B.

At step 116, a first interval of the drying or desiccation phase begins,such as where tissue modification occurs, in which control circuit 48causes electrical-energy source 44 to provide a first drying signal,such as a first drying pulse, to the engaged biological tissue duringthe first drying interval of the drying phase. Power (W) of the providedfirst drying signal is controlled according to a first drying scheduleor plan, such as using a pre-defined power curve, such as having alinear ramp rate. In some examples, the first drying schedule or plan isa monotonically-increasing power schedule, such as shown in the bottomgraph in FIG. 4 between times t₁ and t₂.

Then, at step 118, control circuit 48 compares the provided power to afirst threshold value, such as a first predetermined maximum power. If,at step 118, the provided power is greater than the first predeterminedmaximum power, then the method advances to step 130 illustrated in FIG.3B, such as shown in the bottom graph in FIG. 4 between times t₂ and t₃,which depicts a second drying interval of the drying phase. In someexamples that include a second drying interval, the control circuit 48can reduce the ramp rate at block 130, such as shown in the bottom graphin FIG. 4 between times t₂ and t₃. In this manner, the control circuit48 can modify the energy delivery during a first pulse, such as a firstdrying pulse, in response to the measured, e.g., intermittently, firstelectrical parameter of the engaged biological tissue meeting a firstthreshold value.

The system can measure, e.g., intermittently, the first electricalparameter, such as an electrical current and, in response to themeasured electrical current of the engaged biological tissue satisfyinga first threshold value, such as a predetermined value, reduce orterminate the energy delivery during the therapeutic phase. In someexamples, the predetermined value is an absolute current thresholdvalue. In some examples, the predetermined value is a threshold valuethat can change depending on a pulse count. In some examples, thepredetermined value is a change in current relative to an initialcurrent measurement. In some examples, the predetermined value is achange in current relative to a maximum current measurement during apulse of the therapeutic signal.

If, however, at step 118, the provided power is less than the firstpredetermined maximum power, then the method advances to step 120, wherecontrol circuit 48 causes measurement circuit 46 to measure a firstelectrical parameter, such an impedance or an electrical currentconducted by the engaged biological tissue.

At step 122, control circuit 48 compares the measured electrical current(or impedance), e.g., a first electrical parameter, for this pulse withthe maximum electrical current previously measured (if any), e.g., athreshold value. If, at step 122, the measured electrical current isgreater than the maximum electrical current, then the method advances tostep 124, where the measured electrical current is recorded as the newmaximum value, and then the method returns to step 116 so as to continuethe first drying interval of the drying phase by modifying the energydelivery during the first pulse. If, however, at step 122, the measuredelectrical current is less than the maximum electrical current, then themethod advances to step 126, where control circuit 48 compares themeasured electrical current with a predetermined fraction of the maximumelectrical current.

If, at step 126, the measured electrical current, e.g., a measured firstelectrical current, is greater than the predetermined current threshold,e.g., a measured second electrical current, then the method returns tostep 116 so as to continue the first drying interval of the dryingphase. In some examples, the predetermined current threshold can be aratio or fraction of the maximum electrical current, such as 0.9, 0.8,0.66, 0.5, and 0.4. for example. In other words, control circuit 48 cancontinue the drying signal or pulse in response to a ratio of themeasured first electrical current to the measured second electricalcurrent exceeding a predetermined factor indicating there has not been aphase change of liquid in the engaged biological tissue. In otherexamples, the predetermined current threshold can be a difference ratherthan a ratio.

If, however, at step 126, the measured electrical current is less thanthe predetermined fraction of the maximum electrical current, then themethod advances to step 128, where the first drying pulse of the firstdrying interval of the drying phase is terminated. The method thenreturns to step 104 so as to repeat the interrogation phase, after whichthe drying phase can be repeated or a sealing phase can begin. In otherwords, the system can monitor electrical current during a therapeuticphase to determine when that therapeutic phase should end.

In some examples and in contrast to determining whether the measuredelectrical current is less than the predetermined faction of the maximumelectrical current at step 126, the control circuit 48 can determinewhether the measured electrical current is less than the predeterminedfraction (or offset) of a current value measured at a predetermined timeinterval following the initiation of the pulse. For impedance monitoringsystems, the control circuit 48 can determine whether the measuredimpedance is greater than the predetermined fraction (or offset) of aresistance value measured at a predetermined time interval following theinitiation of the pulse.

At step 130 (depicted in FIG. 3B), a second interval of the drying phasebegins, in which control circuit 48 causes electrical-energy source 44to provide a second drying signal, such as a second drying pulse, to theengaged biological tissue during the second drying interval of thedrying phase. It should be noted that although first and second dryingintervals of a drying phase are shown in FIGS. 3A and 3B, there need notbe a second drying interval of the drying phase. Rather, in someexamples, the drying phase can terminate during the first dryinginterval. Power (W) of the provided second drying signal, such as asecond drying pulse, is controlled according to a second drying scheduleor plan, such as using a pre-defined power curve. In a power-controlled(or voltage-controlled or current-controlled) technique, the system cancontrol the setting of the actuation energy level. Power (or voltage orcurrent) constraint refers to a ceiling or threshold that the controlledcurrent is not to cross, or there is an error state.

In other examples, Voltage (V) across the engaged biological tissue iscontrolled during the second drying interval. In a voltage-controlledtechnique, the system can control the setting of the actuation energylevel. Voltage constraint refers to a ceiling or threshold that thecontrolled voltage is not to cross, or there is an error state. Involtage-controlled implementations, the control circuit can monitor thevoltage of the therapeutic signal and when the threshold or ceiling ismet, the control circuit can maintain the voltage at the threshold. Insome voltage-controlled implementations, the voltage can be capped at aceiling. In other voltage-controlled implementations, the voltage can betime variant.

In the depicted example, the second drying interval uses a second dryingschedule or plan that is a monotonically-increasing power schedule. Insome examples, for example, the second drying schedule or plan is alinearly-increasing power schedule. Then, at step 132, control circuit48 compares the provided power to a second predetermined maximum power.If, at step 132, the provided power is greater than the secondpredetermined maximum power, then the method advances to step 134, wherecontrol circuit 48 causes electrical-energy source 44 to provide powerequal to the second predetermined maximum power, e.g., a power ceiling,and then method 100 advances to step 136. If, however, at step 132, theprovided power is less than the second predetermined maximum power, thenthe method advances to step 136, where control circuit 48 causesmeasurement circuit 46 to measure electrical current conducted by theengaged biological tissue.

At step 138, control circuit 48 compares the measured electrical currentwith maximum current previously measured. If, at step 138, the measuredelectrical current is greater than the maximum electrical current, thenthe method advances to step 140, where the measured electrical currentis recorded as the new maximum value, and then the method returns tostep 130 so as to continue the second drying phase. If, however, at step138, the measured electrical current is less than the maximum electricalcurrent, then the method advances to step 142, where control circuit 48compares the measured electrical current with a predetermined fractionof the maximum electrical current. If, at step 142, the measuredelectrical current is greater than the predetermined ratio or fractionof the maximum electrical current, then the method returns to step 130so as to continue the second drying interval of the drying phase. Inother words, control circuit 48 can reduce the drying signal or pulse inresponse to a ratio of the measured first electrical current to themeasured second electrical current exceeding a predetermined factorindicating a phase change of liquid in the engaged biological tissue. Inother examples, the predetermined current threshold can be a difference.If, however, at step 142, the measured electrical current is less thanthe predetermined faction of the maximum electrical current, then themethod can exit the second interval of the drying phase and return tostep 104 so as to repeat the interrogation phase, after which the dryingphase can be repeated or a sealing phase can begin. In other words, thesystem can monitor electrical current during a therapeutic phase todetermine when that therapeutic phase should end.

At step 146, a sealing or coagulation phase begins in which controlcircuit 48 causes electrical-energy source 44 to provide a sealingsignal, such as a sealing pulse, e.g., a second pulse, to the engagedbiological tissue during the sealing phase, such as shown in the bottomgraph in FIG. 4 between times t₇ and t₈. Power (W) of the providedsealing signal, such as a sealing pulse, is controlled according to asealing schedule or plan. In some examples, the sealing schedule or planis a monotonically-increasing power schedule. Then, at step 148, controlcircuit 48 compares the provided power to a third predetermined maximumpower. It should be note that this is an example of a predeterminedpower curve, which happens to have a constant power domain. If, at step148, the provided power is greater than the third predetermined maximumpower, then the method advances to step 150, where control circuit 48causes electrical-energy source 44 to provide power equal to the thirdpredetermined maximum power, and then method 100 advances to step 152 tomeasure, e.g., intermittently, a second parameter of the engagedbiological tissue, such as the resistance of the tissue. If, however, atstep 148, the provided power is less than the third predeterminedmaximum power, then the method advances to step 152, where controlcircuit 48 causes measurement circuit 46 to measure electricalresistance of the engaged biological tissue.

At step 154, control circuit 48 compares the measured electricalresistance with a second threshold value, such as a calculatedtermination resistance value. In some examples, the calculatedtermination resistance value resistance is calculated based on thereference resistance measured at step 106, e.g., the first resistance.For example, the termination resistance value can be a predeterminedfactor times the measured reference resistance. In some examples, thetermination resistance value can be a sum of a predetermined resistancedelta and either the measured reference resistance or a minimum value ofthe resistance measured during that phase or a previous phase. In someexamples, the target resistance is the predetermined delta resistance,where the predetermined delta resistance is a change in resistancerelative to a minimum resistance measurement during a pulse of thetherapeutic signal.

If, at step 154, the measured electrical resistance is less than thecalculated termination resistance, then the method returns to step 146so as to continue the sealing phase. If, however, at step 154, themeasured electrical resistance is greater than the calculatedtermination resistance, then the sealing phase is terminated, and themethod ends. In other words, in response to the measured, e.g.,intermittently, impedance meeting a second threshold value, such aschanging by a predetermined delta impedance value, for example, themethod can modify the energy delivery of the second pulse, such as byreducing or terminating the energy delivery during this therapeuticphase, such as a sealing phase.

In some non-limiting examples, the method shown in FIGS. 3A and 3B canbe implemented by a system such that the control circuit can monitor afirst electrical parameter, such as an electrical current, in a firsttherapeutic phase, such as a drying phase, and reduce or terminate afirst pulse based on the first electrical parameter, and monitor asecond electrical parameter, such as an impedance, in a secondtherapeutic phase, such as a sealing phase, and reduce or terminate asecond pulse based on the second electrical parameter.

FIG. 4 is a graph depicting non-limiting examples of anelectrotherapeutic schedule or plan used to control electrical powerprovided to biological tissue being sealed. In FIG. 4, Graph 200 hashorizontal axis 202, vertical axes 204A-204C, and functional relations206A-206C. Horizontal axis 202 is indicative of time (seconds).Horizontal axis has times t₀-t₈, which signify transition times betweenthe interrogation, drying, and sealing phases disclosed in thediscussion pertaining to method 100 for generating an electrotherapeuticsignal for treating a biological tissue engaged by an electrosurgicalinstrument. These phases—the interrogation, first drying, and sealingphases—are also notated at various locations of graph 200. It should benoted that the graph of FIG. 4 is meant for purposes of explanationonly. The graph of FIG. 4 depicts an example of a response and differenttissues can react differently.

Vertical axis 204A is indicative of electrical power (W) provided tobiological tissue engaged by an electrosurgical instrument. Functionalrelation 206A indicates a non-limiting example of a power/time relationcorresponding to the electrotherapeutic signal generated based on thenon-limiting example of a method 100 illustrated in FIGS. 3A-3B.Vertical axis 204B is indicative of electrical current conducted by theengaged biological tissue. Functional relation 206B indicates theelectrical current/time relation pertaining to the electrical currentconducted by the engaged biological tissue to which theelectrotherapeutic signal generated via method 100 is provided. Verticalaxis 204C is indicative of electrical resistance of the engagedbiological tissue. Functional relation 206C indicateselectrical-resistance/time relation corresponding to the electricalresistance of the engaged biological tissue to which theelectrotherapeutic signal generated via method 100 is provided.

In some examples, the functional relation 206A can be a pre-definedpower curve, including an interrogation phase, a drying phase, and asealing phase. In the specific non-limiting example shown in FIG. 4, thedrying phase depicts first and second drying intervals. From times t₀ tot₁, power/time relation 206A indicates the interrogation phase. In someexamples, the duration of the interrogation phase is as short as isneeded to obtain a reference measurement of the engaged biologicaltissue. For example, the duration of the interrogation phase can be lessthan 1.0, 0.5, 0.25, or 0.1 seconds. As indicated in graph 200, theinterrogation phase is a constant-power schedule or plan having power P1(W). From times t₀ to t₁, electrical current/time relation 206Bindicates an interrogation rapid electrical current rise, followed by anelectrical current plateau, which is then followed by a slight decreasein electrical current conducted by the engaged biological tissue.Because power is controlled to be constant throughout this interrogationphase, the voltage applied across the engaged biological tissue isinversely related (in a multiplicative sense as opposed to an additivesense) to the electrical current/time relation. The resistance of theengaged biological tissue can initially decrease as the temperature ofthe fluid in the tissue increases. Because this is the first time theinterrogation phase is performed, the measured electrical resistance isnot less than a minimum resistance previously measured, and thereforethe method advances to the first drying phase.

From times t₁ to t₂, power/time relation 206A indicates the firstinterval of the drying phase. As indicated in graph 200, the firstdrying interval of the drying phase is an electrical-power schedule orplan that monotonically increases from powers P1 to P2 (W). From timest₁ to t₂, electrical current/time relation 206B indicates electricalcurrent conducted by the engaged biological tissue increases throughoutthe first interval of the drying phase. Because power is controlledthroughout this first interval of the drying phase according to a dryingschedule or plan, a product of the voltage applied across the engagedbiological tissue and the electrical current/time relation should yieldpower/time relation 206A. Although not depicted, in some examples, theelectrical-resistance/time relation 206C can indicate that electricalresistance of the engaged biological tissue initially can decrease asthe tissue warms, but then can increase as the tissue begins to dryduring the first interval of the drying phase. Such increasingelectrical resistance can indicate drying of the engaged biologicaltissue. Because the electrical current does not decrease below afraction of a previously measured maximum electrical current beforepower/time relation 206A ramps to a predetermined threshold, the methodadvances to the second interval of the drying phase. If the current wereto have dropped below the fraction of the previously measured maximumelectrical current during this first interval of the drying phase, thesubsequent second interval of the drying phase would not be necessary(e.g., it could be bypassed).

From times t₂ to t₃, power/time relation 206A indicates the secondinterval of the drying phase. As indicated in graph 200, the secondinterval of the drying phase is an electrical-power schedule or planthat monotonically increases from powers P2 to P3 (W). Using thetechniques described above with respect to FIGS. 3A and 3B, a controlcircuit, such as the control circuit 48 of FIG. 2, can control an energydelivery of the therapeutic signal provided to the biological tissueduring a portion of a therapeutic phase according to an incrementalchange in energy delivery as a function of a change in a measuredelectrical parameter of the biological tissue. For example, a controlcircuit can incrementally modify the power as a function of current. Insome examples, the function of current is a function of an instantaneousmeasured change in current. In some examples, the function of theinstantaneous measured change in current is a linear function. In otherexamples, the control circuit can incrementally modify the power as afunction of resistance.

From times t₂ to t₃, electrical current/time relation 206B indicateselectrical current conducted by the engaged biological tissue increasesat the beginning of the second interval of the drying phase, but peaksand then decreases at the end of the second drying phase. It should benoted that a second interval of the drying phase may not be needed. Insome examples, power can be controlled throughout this second intervalof the drying phase such that a product of the voltage applied acrossthe engaged biological tissue and the electrical current/time relationcan yield a particular power/time relation 206A.

In some examples, the second interval of the drying phase ismonotonically increasing, but at a slower rate of increase than that ofthe first interval of the drying phase. In other examples, the secondinterval of the drying phase is linearly increasing until the providedpower equals a predetermined maximum level, after which time theprovided power is held constant. Because the decrease in electricalcurrent ΔI1 e.g., a measured change in current (such as at block 126 inFIG. 3A), results in a current that is less than a predeterminedfraction of the maximum electrical current measured, the method returnsto the interrogation phase, which is shown at time t₃. In other words,the change in electrical current ΔI1 causes the method to enter theinterrogation phase at time t₃. It should be noted that in thenon-limiting example shown in FIG. 4, the change in electrical currentΔI1 that causes the method to enter the interrogation phase is aftertime t₂. However, in other examples, the change in electrical currentΔI1 that causes the method to enter the interrogation phase can be aftertime t₁ during the first interval of the drying phase, and a secondinterval of the drying phase may not be needed. If, however, thedecrease in electrical current ΔI1 had instead been less than thepredetermined fraction of the maximum electrical current measured, thenthe method would have remained in the drying phase.

As seen in FIG. 4, in some examples, the pre-defined power curve 206Acan include two or more linear portions, such as shown between t₁ and t₂and between t₂ and t₃.

From times t₃ to t₄, power/time relation 206A depicts the interrogationphase again. As indicated in graph 200, the interrogation phase is aconstant-power schedule of power P1 (W). Because power is controlled tobe constant throughout this interrogation phase, the voltage appliedacross the engaged biological tissue is inversely related (in amultiplicative sense as opposed to an additive sense) to the electricalcurrent/time relation. Electrical-resistance/time relation 206Cindicates that the electrical resistance of the engaged biologicaltissue is decreasing throughout this performance of the interrogationphase. Decreasing electrical resistance can be a result of condensing offluid in the tissue or migration of fluid into the tissue. Because themeasured electrical resistance is not greater than a sum of thereference resistance and a predetermined delta resistance, the methodadvances again to the first drying phase.

From times t₄ to t₅, power/time relation 206A indicates another firstinterval of the drying phase. The power/time relation from times t₄ tot₅ is similar to the power/time relation 206A from times t₁ to t₂ and,for purposes of conciseness will not be described in detail again.

From times t₅ to t₆, power/time relation 206A indicates another secondinterval of the drying phase. The power/time relation from times t₅ tot₆ is similar to the power/time relation 206A from times t₂ to t₃ and,for purposes of conciseness will not be described in detail again.Because power is controlled to be constant throughout this secondinterval of the drying phase, a product of the voltage applied acrossthe engaged biological tissue and the electrical current/time relationshould yield power/time relation 206A. Because the decrease inelectrical current ΔI2, e.g., a measured change in current (such as atblock 142 in FIG. 3B), is less than a predetermined fraction of themaximum electrical current measured, the method returns to theinterrogation phase.

From times t₆ to t₇, power/time relation 206A indicates anotherinterrogation phase. The power/time relation from times t₆ to t₇ issimilar to the power/time relation 206A from times t₃ to t₄ and, forpurposes of conciseness will not be described in detail again. Becausethe measured electrical resistance is now greater than a sum of thereference resistance and a predetermined delta resistance, the methodadvances to the sealing phase.

From times t₇ to t₈, power/time relation 206A indicates the sealingphase. As indicated in graph 200, the sealing phase is anelectrical-power schedule or plan that monotonically increases frompower P1 to power P3 (W). From times t₇ to t₈, electrical current/timerelation 206B indicates an increasing electrical current conducted bythe engaged biological tissue throughout the sealing phase.Electrical-resistance/time relation 206C indicates that the electricalresistance of the engaged biological tissue is increasing thisperformance of the sealing phase. Increasing electrical resistance canbe a result of drying and thereby sealing of the engaged biologicaltissue. Because the measured electrical resistance is now greater than apredetermined termination resistance, the sealing phase is terminated,and the method ends.

Predictive Phase Control of an Electrotherapeutic Signal (FIGS. 5-6)

An electrosurgical procedure can have one or more electrotherapeuticphase. For example, an electrosurgical tissue-sealing technique can havean interrogation phase, a drying phase, and/or a sealing phase. Duringeach of these electrotherapeutic phases, a correspondingelectrotherapeutic signal, such as, for example, an interrogationsignal, a heating signal, a drying signal, a cauterizing signal, etc.,can be provided to biological tissue engaged by an electrosurgicalinstrument. The electrotherapeutic signal provided to the engagedbiological tissue can be tailored to the technique being performedand/or to the specific tissue. Thus, each electrosurgical signal can bedifferent for different procedures, for different tissue types andquantities, and for different electrotherapeutic phases. Thesedifferences in different electrotherapeutic signals can be obtainedusing different electrotherapeutic schedules and/or differentphase-control criteria. Differences between different electrotherapeuticschedules can arise from differences in controlled electricalparameters, and/or differences in phase control criteria. As describedabove, differences in controlled electrical parameters include apparentpower (VA), real power (W), voltage (V) and/or electrical current (A) ofthe electrotherapeutic signal. Phase-control criteria include criteriafor commencement and termination of a phase, as well as criteria forintra-phase control. Such phase-control criteria include contemporaneousphase-control criteria and predictive phase-control criteria.

Contemporaneous phase-control is performed by using a real-timemeasurement to control a phase. Predictive phase-control is performed byusing a reference measurement taken at a reference time to generate afuture phase-control criteria. For example, a tissue-resistancemeasurement taken before or during a drying phase can be used togenerate a time duration for continuing the drying phase. In someexamples, a tissue-resistance measurement can be used to select one of aplurality of predetermined electrotherapeutic schedules. The selectedone of the plurality of predetermined electrotherapeutic schedules canbe used in a subsequent electrotherapeutic phase.

The reference measurement of tissue resistance can be indicative of avessel size, for example. Different size vessels can be heated usingdifferent electrotherapeutic schedules or plans, and/or differentphase-control criteria. Appropriate electrotherapeutic schedules orplans customized for vessel sizes can lead to more secure sealing andless trauma to nearby tissue. To ensure proper sealing of the engagedvessel, the electrotherapeutic schedule can be tailored according tosize of the vessel to be sealed. The vessel size can be estimated basedon a measured reference resistance of the engaged vessel. Vessel sealingcan then proceed according to the electrotherapeutic schedule that isdetermined based on the measured reference resistance of the engagedvessel.

Described below with respect to FIG. 6 are, among other things,techniques for predicting and delivering energy based on the size of thetissue detected. After an electrosurgical generator, such aselectrosurgical generator 12 of FIG. 2, delivers an initial applicationof energy to the biological tissue via an electrosurgical device, acontrol circuit, such as the control circuit 48 of FIG. 2, and ameasurement circuit, such as the measurement circuit 46 of FIG. 2, canmeasure or calculate the tissue impedance at a point in time. Thecontrol circuit can then determine the type of tissue, e.g., smallvessel or large vessel, in contact with the electrosurgical device, suchas between the jaws of electrosurgical device, and then deliver energyfor the type of tissue that has been detected.

FIG. 6 is a flow chart of a biological vessel-sealing method that usesan electrical-power schedule corresponding to a size of biologicalvessel engaged by the electrosurgical instrument. The method FIG. 6 usesthree therapeutic phases: Phase 1 is an interrogation phase, Phase 2 isa desiccation or drying phase, and Phase 3 is a vessel welding phase. InPhase 1, the electrosurgical system, such as the electrosurgical system10 of FIG. 1, can perform error checking and generate and deliver aninterrogation signal to the engaged tissue, such as according to aninterrogation schedule. Although described in FIG. 6 as beingvoltage-controlled, the control circuit can deliver the energy usingeither power-controlled techniques or voltage-controlled techniques. Involtage-controlled techniques, current can be capped but allowed to movefreely according to the responding impedance, which can allow for avariable power delivery.

Using the techniques of this disclosure, the method can begin a phase,such as Phase 2, without the control circuit having determined whatcriteria it will use to terminate the phase. For example, as describedin more detail below, the method starts Phase 2 and the control circuit,and the measurement circuit can determine an impedance measurement ofthe tissue. In response, the control circuit can determine whether toterminate Phase 2 based on a time measurement or based on iterativeimpedance measurements. In this manner, the control circuit has twodistinct criteria for how it will terminate the Phase 2 but enters Phase2 without having already selected which of the two criteria to use.

At block 1900, Phase 1 starts and, at block 1901, the control circuitand the measurement circuit can measure and/or calculate an initialimpedance value R0 at time T0. At block 1902, the control circuit canset the voltage ramp rate or slope for Phase 2. The voltage setting canbe a constant voltage, an increasing voltage, or a decreasing voltage.Again, for power-controlled implementations, the control circuit can setthe power ramp rate or slope for Phase 2. The power can be a constantpower, an increasing power, or a decreasing power. The output of thePhase 1 is the initial impedance value R0 .

At block 1904, Phase 2 begins. At block 1906, after a set period oftime, the control circuit and the measurement circuit can measure orcalculate a reference impedance R1. The impedance of the tissue can havechanged from the initial impedance R0 to the impedance R1. The impedanceR1 is measured to determine whether Phase 2 will be an open loop phase(terminated based on a temporal criterion, such as by a timer expiring)or a closed loop phase (terminated based on an impedance criterion, forexample). For drier tissue, running Phase 2 as an open loop can bedesirable whereas for wetter tissue, running Phase 2 as a closed loopcan be desirable.

At block 1908, the control circuit can determine whether the impedanceR1 is greater than or equal to a threshold impedance value Ra. In someexamples, the impedance Ra can be absolute impedance. In other examples,the impedance Ra can be a delta value, such as a predetermined rise fromthe initial measured impedance R0. In some examples, the impedance Racan be about 90 ohms.

In some examples, in addition to or instead of comparing a measuredimpedance R1 to a threshold impedance Ra, the control circuit cancompare some other measured parameter to a threshold parameter. Forexample, the control circuit can compare a measured phase angle to athreshold phase angle. Examples of other parameters that can be usedinclude, but are not limited to, the energy delivered over a period oftime, current draw, tissue temperature, and the like.

If the control circuit determines that the impedance R1 is greater thanor equal to the impedance Ra (“YES” branch of block 1908), then thecontrol circuit can run Phase 2 as an open loop at block 1910 andcontinue delivering power until a timer expires at a time T2. At block1912, Phase 2 ends based on a temporal criterion, such as by a timeinterval.

However, if the control circuit determines that the impedance R1 is notgreater than or equal to the impedance Ra (“NO” branch of block 1908),then the control circuit can run Phase 2 as a closed loop starting atblock 1914. At block 1916, the control circuit can measure an impedanceR2N at a set time interval. At block 1918, the control circuit candetermine whether the present impedance measurement R2N is greater thanor equal to an impedance threshold value R2X.

If the control circuit determines that the impedance R2N is not greaterthan or equal to the impedance R2X (“NO” branch of block 1918), then themethod can continue applying power and return to block 1914. The methodcan repeat the impedance measurement at a time interval at block 1916and determine whether the new impedance measurement is greater than orequal to the threshold at block 1918. In this manner, the method cancontinue applying power and iteratively comparing an impedancemeasurement to a threshold impedance value.

If the control circuit determines that the impedance R2N (or any of thesubsequent impedance measurements, if needed) is greater than or equalto the impedance R2X (“YES” branch of block 1918), then the controlcircuit can terminate Phase 2 at block 1920 based on an impedancecriterion (in contrast to the time criterion described above for theopen loop process).

After the control circuit terminates Phase 2, regardless of whetherPhase 2 terminated based on time or an impedance measurement, thecontrol circuit can calculate and store an impedance measurement R3 atblock 1922. Next, at block 1924, the control circuit can determinewhether the present impedance measurement R3 is less than or equal to animpedance threshold value RX.

If the control circuit determines that the impedance R3 is greater thanor equal to the impedance RX (“YES” branch of block 1924), then thetissue is a small vessel and the method can start Phase 3 at block 1926.At block 1928, the control circuit can run Phase 3 as an open loop andcontinue delivering power until a timer expires at a time T3. At block1930, Phase 3 ends based on a time interval.

However, if the control circuit determines that the impedance R3 is notgreater than or equal to the impedance RX (“NO” branch of block 1924),then the tissue is a large vessel and the method can start Phase 3 atblock 1932 and the control circuit can run Phase 3 as a closed loop. Atblock 1934, the control circuit can measure an impedance R3N at a settime interval. At block 1936, the control circuit can determine whetherthe present impedance measurement R3N is greater than or equal to animpedance threshold value R3X.

If the control circuit determines that the impedance R3N is not greaterthan or equal to the impedance R3X (“NO” branch of block 1936), then atblock 1938 the control circuit can determine whether a maximum timelimit has been reached. If the control circuit determines that themaximum time limit has been reached (“YES” branch of block 1938), thenthe control circuit can terminate Phase 3 at block 1940. In someexamples, the time limit can be an elapsed time from the start of Phase1.

However, if the control circuit determines that the maximum time limithas not been reached (“NO” branch of block 1938), then the controlcircuit can continue applying power and return to block 1934. The methodcan repeat the impedance measurement at a time interval at block 1934and determine whether the new impedance measurement is greater than orequal to the threshold impedance value R3X at block 1936. In thismanner, the method can continue applying power and iteratively comparingan impedance measurement to the threshold impedance value R3X.

If the control circuit determines that the impedance R3N is greater thanthe impedance R3X (“YES” branch of block 1936), then at block 1942 thecontrol circuit can terminate Phase 3 based on an impedance measurement(in contrast to the time criterion described above for the open loopprocess of Phase).

Correction of Measured Electrical Resistance of Engaged BiologicalTissue (FIGS. 7A-7B and 9)

The various electrical measurements described above can be used in thedetermination of an electrotherapeutic schedule and/or in thedetermination of phase-control criteria. As such, accurate measurementsfacilitate the generation of an electrotherapeutic signal that willsucceed in its therapeutic purpose. Temperatures of an electrosurgicalinstrument and of biological tissue engaged thereby affect electricalmeasurements of the engaged biological tissue. Suchtemperature/measurement relations can introduce uncertainty and/orcomplication in using such electrical measurements in determining anelectrotherapeutic schedule and/or phase-control criteria. For example,comparison of two electrical measurements of an engaged tissue takenwhen the engaged tissue and/or the electrosurgical instrument is atdifferent temperatures can be complicated.

Some examples correct electrical measurements of engaged tissue so as toaccount for temperatures of electrosurgical instruments and/or ofbiological tissues. Measured electrical resistance of biological tissue,for example, can be corrected based on actual temperature measurementsof the electrosurgical instrument. In some examples the electrosurgicalinstrument will be equipped with a temperature sensor in thermalcommunication with the distal end that engages the biological tissue. Inother examples, the measured electrical resistance of biological tissuecan also be corrected based on predicted temperature of the tissueand/or the electrosurgical instrument base on various indirectmeasurements. For example, measured tissue resistance can be correctedbased on a time interval between a reference time and a measurementtime, between which electrical power has been delivered to thebiological tissue. In some examples the measured tissue resistance canbe corrected based on calculation of energy provided to the engagedtissue prior to the electrical measurement.

FIG. 7A is a graph depicting measured tissue resistance as a function ofjaw temperature of a forceps. In FIG. 7A, graph 400 includes horizontalaxis 402, vertical axis 404 and electrical-resistance/temperaturerelation 406. Horizontal axis 402 is indicative of jaw temperature of aforceps. Vertical axis 404 is indicative of measured electricalresistance of a tissue clamped between opposable jaw members of aforceps, such as forceps 14 depicted in FIG. 1.Electrical-resistance/temperature relation 406 depicts measurements of aspecific biological tissue clamped by the opposable jaw members, whichhave been heated to various temperatures.Electrical-resistance/temperature relation 406 depicts amonotonically-decreasing function, in which the measured electricalresistance decreases as jaw temperature increases. Such variations inmeasured electrical resistance can arise from many factors, includingelectrical resistance dependencies on tissue temperature, tissue-liquidphase, jaw-tissue interface, jaw temperature, etc.

Such variations in measured tissue resistance can introduce uncertaintyand/or complication in using such measured electrical resistance todetermine an electrotherapeutic schedule and/or phase-control criteria.Some of the electrical resistance dependencies are undesirable, in thatthey are not indicative of therapeutic effects upon the biologicaltissue. Therefore, compensation of these undesirable dependencies canimprove the quality of such electrical resistance measurements. Variousmethods of compensating electrical measurements of biological tissue canbe performed so as to provide measurements that better indicate thetherapeutic effects of an electrotherapy treatment.

FIG. 7B is a graph depicting jaw temperature vs. time after terminationof power application. In FIG. 7B, graph 410 includes horizontal axis412, vertical axis 414 and temperature-time relation 416. Horizontalaxis 412 is indicative of time after application of anelectrotherapeutic signal has been provided to a biological tissue.During this post-therapy time, no power is delivered to the biologicaltissue. Vertical axis 414 is indicative of measured temperature of theopposable jaw members of a forceps used to provide theelectrotherapeutic signal to the tissue. Temperature-time relation 416depicts measurements of jaw temperature at various post-therapy times.Temperature-time relation 416 is a monotonically-decreasing function oftime that asymptotically approaches room temperature. Such atemperature-time relation can be characterized by a time constantindicative of a rate of decay.

The relations depicted in graphs 400 and 410 can be used in modeling thejaw temperature as a function of power application and time durationpost-power application. For example, the power dissipated by biologicaltissue engaged by an electrosurgical instrument can be used to predicttemperature of that biological tissue, as well as the temperature of theengaging portion (e.g., opposable jaw members 36 and 38 depicted inFIG. 1) of the electrosurgical instrument. Such jaw temperature-powerapplication relation can be determined theoretically (e.g., using thetissue volume within the engagement of the opposable jaw members) aswell as empirically (e.g., by characterizing the instrument). In someexamples, the position of the engaged jaw members can be used indetermining the tissue volume within the engagement of the jaw members,for example. In some examples, combinations of theoretical and empiricalcharacterization can be used to model the relation between jawtemperature and power application. The jaw temperature-time post-therapycan similarly be characterized empirically and/or theoretically.

Furthermore, the electrical resistance dependencies that areundesirable, in that they are not indicative of therapeutic effects uponthe biological tissue, can be characterized empirically and/ortheoretically. These various characterizations or models can then becombined to determine a compensated resistance value, based on themeasured resistance value. For example, measurements of tissueresistance taken during application of an electrotherapeutic signal tothe biological tissue can use a calculated jaw temperature based on theelectrotherapeutic schedule for compensation. After application of theelectrotherapeutic signal to the biological tissue, measurements oftissue resistance can be compensated using a post-therapy time duration.

FIG. 8 is a graph depicting electrical resistance compensation vs. timeafter power application. In FIG. 8, graph 420 includes horizontal axis422, vertical axis 424 and delta resistance/time relation 426.Horizontal axis 422 is indicative of time after application of anelectrotherapeutic signal has been provided to a biological tissue.During this post-therapy time, no power is delivered to the biologicaltissue. Vertical axis 424 is indicative of delta resistance needed tocompensate the measured tissue resistance. In some examples, instead ofusing an additive delta-resistance corrective, a multiplicative factorcan be used. Delta-resistance/time relation 426 depicts thedelta-resistance correction factor need to compensate for jawtemperature at various post-therapy times. Delta-resistance/timerelation 426 is a monotonically-decreasing function of time thatasymptotically approaches zero.

In one example, measured tissue resistance can be compensated whenelectrosurgical instrument is hotter that a predetermined threshold, butnot when the electrosurgical instrument is cooler than the predeterminedthreshold. FIG. 8 depicts operating zones 428 and 430, delimiting thesetwo compensation regimes (e.g., hot and cold instrument regimes).Operating zone 428 spans from times immediately after application ofelectrotherapeutic signal to a biological tissue until a predeterminedtime post-application of the electrotherapeutic signal to a biologicaltissue. During this hot-instrument regime, measurements of tissueresistance are compensated by adding a predetermined delta-resistancevalue to the measured tissue-resistance values. In the example depictedin FIG. 8, the time delimiting the transition from hot instrument tocold instrument regimes is around 30 seconds post-therapy. Nocompensation of measurements of tissue resistance are performed in thecold-instrument regime.

Modification of Initial Impedance (FIG. 9)

The control circuit of an electrosurgical generator, such as the controlcircuit 48 of the electrosurgical generator 12 of FIG. 2, can use apredictive algorithm to generate and deliver an electrotherapeuticsignal to biological tissue engaged to an electrosurgical device, suchas between the jaws of the forceps 14 of FIG. 1. The predictivealgorithm can include multiple phases. For example, Phase 1 can use lowpower energy to initially access the vessel impedance and various energydelivery parameters. Based on the initial impedance determined in Phase1, the system can determine the size of the vessel to be sealed, set theparameters in a Phase 2 to dry the vessel tissue, and provide a properenergy level and duration in a Phase 3 to seal the vessel.

It can be challenging to accurately predict the vessel sizes, however.For example, the initial vessel impedance, which can be used todetermine the vessel sized, can be affected by the jaw temperature ofthe electrosurgical device. The jaw can have a high temperature if theuser tries to seal a second vessel right after sealing a first vessel.The high temperature can affect the initial vessel impedancemeasurement.

The present inventors have recognized a need to reduce the temperatureeffects of the initial impedance measurement and improve vessel sizeprediction. As described in more detail below, the present inventorshave recognized that in some examples, a temperature of the jaw can bedetermined using a temperature sensor coupled to the jaw and then themeasured impedance can be modified using a correction factor based onthe jaw temperature. In other examples, the present inventors haverecognized that the measured impedance can be modified using acorrection factor based on one or both of an elapsed time from aprevious activation or electrical characteristic(s) of the previousactivation. Using the modified impedance value, the electrosurgicalsystem can more accurately predict the size of the vessel, which can beused for determining settings for the electrosurgical generator.

FIG. 9 is a flow diagram of a biological vessel-sealing method that cancompensate measurements of tissue impedance after power application. Atblock 2000, a control circuit and a measurement circuit, such as thecontrol circuit 48 and the measurement circuit 46 (both of FIG. 2) canmeasure, in Phase 1, an initial impedance R0 of the biological tissueengaged to the electrosurgical device, such as the forceps 14 of FIG. 1.At block 2002, the control circuit and the measurement circuit canmeasure, in Phase 1, a temperature of a jaw of the electrosurgicaldevice using a temperature sensor coupled to the jaw.

At block 2004, using the measured impedance and the measured jawtemperature, the control circuit can query a stored data log or set,such as a look-up table, and determine or select a adjusted or correctimpedance that is a modification of the initial impedance R0 to accountfor the temperature of the jaws.

At block 2006, the control circuit can determine a vessel size using thedetermined adjusted impedance. For example, using an algorithm oranother stored data set, the control circuit can determine the vesselsize using the adjusted impedance.

Then, at block 2008, the control circuit can use the determined vesselsize to determine various electrical parameters that define theelectrosurgical signal that the electrosurgical generator will generateand deliver to the biological tissue of the vessel. In some examples,the vessel size can be determined to be either a small vessel or a largevessel and there can be two electrosurgical signal settings thatcorrespond to those two vessel sizes. In other examples, there can becontinuum of vessel sizes and electrosurgical settings that correspondto those vessel sizes.

At block 2010, the control circuit can control the delivery of theelectrosurgical signal to the vessel using the determined signalsettings to perform sealing and the method can end at block 2012.

As shown at block 2014, instead of using the jaw temperature, someexamples can store an elapsed time since the last activation. The longerthe elapsed time, the more the jaws have cooled. In this way, theelapsed time since the last activation can be used as a proxy for thejaw temperature.

At block 2004, the control circuit can use the measured initialimpedance R0 and the elapsed time from the last activation to determinean adjusted impedance. In some examples, the control circuit can comparethe elapsed time to a time T, e.g., 20 seconds, and if the elapsed timeis greater than or equal to T, then the control circuit can use theinitial impedance as the adjusted impedance. However, if the elapsedtime is not greater than or equal to T, then the control circuit can adda compensation value to the initial impedance R0 to determine theadjusted impedance. As an example, the compensation value can be betweenabout 80-90 ohms. It should be noted that the compensation value and thetime T can depend on the design of the jaw.

In some examples, rather than adding a compensation value to determinethe adjusted impedance, the control circuit can query a stored data logor set, such as a look-up table, and determine or select a adjustedimpedance that is a modification of the initial impedance R0 to accountfor the elapsed time since the previous activation.

After the control circuit determines the adjusted impedance, the methodcan proceed to block 2006 and beyond, as described above, to determinethe vessel size, signal settings, and perform vessel sealing.

At block 2014, in some examples, one or more electrical characteristicsfrom the previous activation can be used in addition to the elapsed timesince the last activation. For example, the control circuit can use theamount of energy or a current from the previous activation to determinewhether the previous activation generated a large amount of heat on thejaw. If the activation was accidental or quickly terminated, littleenergy or current would have been delivered to the tissue and the jawwould not be heated significantly.

In some examples, the control circuit can determine the amount of energyfrom the previous activation by integrating the power curve of theprevious activation. In other examples, the control circuit candetermine the amount of energy from the previous activation byretrieving from a stored data set the application time and the averagepower delivered and multiplying the time and average power delivered.The elapsed time information combined with the energy or currentinformation from the previous activation can improve the accuracy of theinitial impedance R0 measurement and can increase the capability of thesystem to determine the vessel size. The elapsed time, temperature, andthe electrical characteristics, such as energy and current, can be moregenerally referred to as “sealing parameters”.

In some examples that use both the elapsed time and an electricalcharacteristic, the control circuit can use the initial impedance R0 asthe adjusted impedance if the electrical characteristic, such as energyor current, is below a threshold value. If the electrical characteristicis not below the threshold value, then the method can then use theelapsed time to determine the adjusted impedance.

If the elapsed time is greater than a threshold, which would indicatedthat the jaws have cooled sufficiently, the control circuit can use theinitial impedance R0 as the adjusted impedance. However, if the elapsedtime is not greater than a threshold, the control circuit can add acompensation value, between about 80-90 ohms, to the initial impedanceR0 to determine the adjusted impedance.

In some examples, rather than adding a compensation value to determinethe adjusted impedance, the control circuit can query a stored data logor set, such as a look-up table, and determine or select a adjustedimpedance that is a modification of the initial impedance R0 to accountfor the elapsed time since the previous activation and an electricalcharacteristic, such as energy or current, from the previous activation.

After the control circuit determines the adjusted impedance, the methodcan proceed to block 2006 and beyond, as described above, to determinethe vessel size, signal settings, and perform vessel sealing.

In the examples described above, if the control system was unable todefinitively determine the elapsed time (and, if used, the electricalcharacteristic, such as energy or current), the control circuit candetermine an adjusted impedance that corresponds with a large vessel.Defaulting to a large vessel setting can enhance the safety of vesselsealing.

By using the techniques described above, the control circuit can deliveran electrotherapeutic signal to biological tissue engaged to theelectrosurgical device, measure an impedance of the engaged biologicaltissue, measure an electrosurgical device sealing parameter, anddetermine an adjusted impedance based on a relationship between theelectrosurgical device sealing parameter and the measured impedance.

Reducing Sticking of Biological Tissue to Electrosurgical Instrument byPulsing Electrical Power of Electrotherapeutic Signal (FIGS. 10A-10D and11)

FIGS. 10A-10D are graphs of electrical parameters of anelectrotherapeutic signal of an electrotherapy having a pulsed stickingreduction portion. In FIG. 10A, graph 500 includes horizontal axis 502,vertical axis 504 and voltage/time relation 506. Horizontal axis 502 isindicative of time. Vertical axis 504 is indicative of voltage of anelectrotherapeutic signal provided to tissue engaged by anelectrosurgical instrument. Voltage/time relation 506 depictsmeasurements of a voltage difference taken at times indicated byhorizontal axis 502. The voltage difference is applied across tissueengaged by an electrosurgical instrument. As shown in graph 500,voltage/time relation has four phases 508A-508D. The first phase 508A isan interrogation phase, during which a modest voltage is provided to theengaged tissue, so as to obtain an initial measurement of tissueresistance.

Following interrogation phase 508A is second phase 508B, which is adrying phase. During drying phase 508B, the voltage difference providedacross the engaged tissue is monotonically increasing. In the depictedexample, the voltage difference provided across the engaged tissue islinearly increasing. In some examples, drying phase 508B will have aninitial slope that is greater than a final slope. In some examples,instead of controlling the voltage difference applied across the engagedtissue during the drying phase, another electrical parameter iscontrolled. For example, in some examples, the current conducted by orthe power (real or apparent) provided to the engaged tissue iscontrolled.

Each of the controlled parameters provides various advantages anddisadvantages as compared with the other controlled parameters. Forexample, controlling the voltage difference across the engaged tissuerequires measurements of only the voltage difference providedthereacross. As the tissue heats, however, the tissue resistancegenerally increases, thereby causing a reduced current to flowtherethrough. The rate of heating is thus slowed as the power providedto the tissue decreases in response to increased tissue resistance.

Controlling the current conducted by the engaged tissue requiresmeasurements of only the current conducted thereby, which can be readilyperformed by measuring voltage through a small series resistor, forexample. As disclosed above, heating of the tissue generally causes anincrease of the tissue resistance, thereby causing an increased voltagedifference thereacross. The rate of heating is thus accelerated as thepower provided to the tissue increases in response to increased tissueresistance.

Controlling real power provided to the engaged tissue, however, requiresmeasurements of both voltage difference across and current conducted bythe engaged tissue. As the tissue heats, and the tissue resistancechanges, both the voltage applied across and the current conducted bythe engaged tissue is adjusted so as to maintain power according to anelectrotherapeutic schedule. The rate of heating is proportional to thepower provided to the engaged tissue, and therefore is controlled, suchas, for example, real power (W) or electrical current (I).

Following drying phase 508B is third phase 508C, which is a sealingphase. During sealing phase 508C, the voltage difference provided acrossthe engaged tissue is constant. In some examples, sealing phase 508Cwill not be constant. In some examples, instead of controlling thevoltage difference applied across the engaged tissue during the sealingphase, another electrical parameter is controlled.

Following sealing phase 508C is fourth phase 508D, which is asticking-reduction phase. During sticking-reduction phase, the voltageis pulsed between voltage maxima and voltage minima. Such pulsingalternately heats and permits cooling of the engaged tissue. Thesticking-reduction plan can have alternating electrical-power minima andmaxima, where each of the electrical-power minima are below apredetermined threshold configured to permit a temperature of theclamped biological tissue to fall below a liquid/gas phase-changethreshold so as to permit liquid to exist in the clamped biologicaltissue. In some examples, each of the electrical-power minima of thesticking-reduction plan is maintained for a first predetermined timeduration. In some examples, the first predetermined time duration isgreater than or equal to 5 milli-seconds. In some examples, the firstpredetermined time duration is greater than or equal to 10milli-seconds. In some examples, the first predetermined time durationis greater than or equal to 50 milli-seconds.

During the cooling portions of the pulsed waveform, liquid, which hadbeen previously driven out of the engaged tissue, can return to theengaged tissue. In the depicted example, the pulsed waveform isperiodic, in that each cycle is identical to the cycle preceding it. Insome examples, the pulsed waveform is not periodic. For example, eachpulse maxima can be less than the preceding pulse maxima.

Sticking-reduction phase 508D can be initiated in various manners.Sticking-reduction phase commences after proper sealing of the engagedtissue has been completed. In some examples, predictive phase controlcan be used to initiate or commence sticking reduction phase 508D. Forexample, tissue resistance can be measured at a reference time duringinterrogation phase 508A, drying phase 508B, or sealing phase 508C. Timeduration of the sealing phase can be predicted based on the tissueresistance measured at the reference time. Sticking reduction phase 508Dcan commence in response to the predicted time duration of the sealingphase having elapsed. In some examples, tissue therapy can continueduring the sticking reduction phase.

In FIG. 10B, graph 510 includes horizontal axis 512, vertical axis 514and tissue-resistance/time relation 516. Horizontal axis 512 isindicative of time. Vertical axis 514 is indicative of electricalresistance of the tissue engaged by an electrosurgical instrument.Tissue-resistance/time relation 516 depicts measurements of tissueresistance taken at times indicated by horizontal axis 512. As shown ingraph 510, tissue resistance is low during interrogation phase 508A,increases during drying phase 508B, and remains high throughout sealingphase 508C. During sticking-reduction phase 508D, tissue resistancealternates between low and high values. The low measurements of tissueresistance obtained at during the minima of the pulsed waveform areindicative of liquid returning to the engaged tissue.

In FIG. 10C, graph 520 includes horizontal axis 522, vertical axis 524and current/time relation 526. Horizontal axis 522 is indicative oftime. Vertical axis 524 is indicative of current conducted by the tissueengaged by an electrosurgical instrument. Current/time relation 526depicts measurements of current taken at times indicated by horizontalaxis 522. As shown in graph 520, current increases at the beginning ofdrying phase 508B, but then decreases at the end of drying phase 508B asthe tissue resistance increases. The current then remains low throughoutsealing phase 508C. During sticking-reduction phase 508D, current issubstantially periodic with maxima that are greater than the currentvalues obtained during sealing phase 508C.

In FIG. 10D, graph 530 includes horizontal axis 532, vertical axis 534and power/time relation 516. Horizontal axis 512 is indicative of time.Vertical axis 514 is indicative of real power of the tissue engaged byan electrosurgical instrument. Power/time relation 516 depictsmeasurements of power provided to engaged tissue taken at timesindicated by horizontal axis 532. As shown in graph 530, power increasesat the beginning of drying phase 508B, but then decreases at the end ofdrying phase 508B as the tissue resistance increases. Duringsticking-reduction phase 508D, power is substantially periodic withmaxima that are greater than the power values obtained during sealingphase 508C. The power has peaks at the beginning of the maxima. Thesepeaks of power correspond to the peaks in current that occur beforeliquid is driven from the engaged tissue.

FIG. 11 is a flow chart of a method for reducing sticking betweenbiological tissue and an electrosurgical instrument. In FIG. 11, method540 begins at step 542, in which biological tissue is engaged by anelectrosurgical instrument. Then, at step 544, control circuit 48(depicted in FIG. 2) causes electrical-energy source 44 (depicted inFIG. 2) to provide an interrogation signal to the engaged biologicaltissue during an interrogation phase. Then, at step 546, control circuit48 causes measurement circuit 46 (depicted in FIG. 2) to measure areference tissue resistance R_(REF). Then at step 548, a therapy timeduration T_(THERAPY) is determined based on the measured referenceresistance R_(REF).

At step 550, control circuit 48 causes electrical-energy source 44 toprovide an electrotherapeutic signal to the engaged biological tissueduring an electrotherapeutic phase. Then, at step 552, an elapsedtherapy time T_(ELAPSED) is compared with the therapy time durationT_(THERAPY) determined at step 548. If, at step 552, the elapsed therapytime T_(ELAPSED) is less than the determined therapy time durationT_(THERAPY), then the method returns to step 550, where theelectrotherapeutic signal is provided to the engaged biological tissue.If, however, at step 552, the elapsed therapy time T_(ELAPSED) isgreater than the determined therapy time duration T_(THERAPY), thenmethod 540 advances to step 554, where control circuit 48 causeselectrical-energy source 44 to provide a pulsed sticking-reductionsignal to the engaged biological tissue during a sticking reductionphase. After the sticking-reduction phase, the method ends. The pulsedsticking-reduction signal can be determined according to asticking-reduction schedule. The sticking reduction schedule can beconfigured to reduce sticking, and in some examples to simultaneouslyprovide additional tissue therapy.

Determining Presence or Absence of a Conductive Foreign Body inBiological Tissue Engaged by an Electrosurgical Instrument (FIGS. 12 and13)

In various surgical procedures, artificial devices are implanted into apatient. For example, broken bones can be set with screws, bolts, shims,and other mechanical members. Staples can be used to maintain a desiredarrangement of tissues that have been treated during surgery. Pacemakersand other electronic devices can be implanted into the patient forvarious purposes. Many of these artificial devices are or containelectrically conductive elements. Electrically conductive objects caninterfere with electrosurgical procedures, should one be found in tissueengaged by the electrosurgical instrument.

Determining an environmental condition of the electrosurgicalinstrument, such as a presence or absence of a conductive foreign bodywithin the engaged tissue before providing an electrotherapeutic signalto the engaged tissue, can prevent undesirable tissue modification.Presence or absence of a conductive foreign body in biological tissueengaged by an electrosurgical instrument can be determined based onangle of an impedance measurement of the engaged biological tissue.Therefore, interrogation of the angle of tissue impedance before anelectrotherapeutic phase can prevent such undesirable tissuemodification.

FIG. 12 is a graph depicting examples of impedance-angle/time relationsof biological tissues with and without metal objects therein. In FIG.12, graph 600 includes horizontal axis 602, vertical axis 604 andimpedance-angle/time relations 606A-606B. Horizontal axis 602 isindicative of time. Vertical axis 604 is indicative of impedance angleof a biological tissue engaged by an electrosurgical instrument.Impedance-angle/time relations 606A-606B depicts measurements of animpedance angle taken during an electrotherapeutic phase at timesindicated by horizontal axis 602. The impedance angle of the biologicaltissue is indicative of the ratio of a reactive component of the tissueimpedance to the resistive component of the tissue impedance. Forexample, an impedance angle of −90° indicates purely capacitive tissueimpedance, an impedance angle of +90° indicates purely inductive tissueimpedance, and an impedance angle of 0° indicates purely resistivetissue impedance. In some examples, a measured reference impedance angleis substantially equal to an angular difference between a voltage acrossand current conducted by the engaged biological tissue as measured by ameasurement circuit.

Impedance-angle/time relation 606A corresponds to a tissue in which noconductive foreign body is present. Impedance-angle/time relation 606Bcorresponds to a tissue in which a conductive foreign body is present.As shown in graph 600, both of impedance-angle/time relations 606A and606B indicate the impedance angle changes during an initial or transientportion of the electrotherapeutic phase, and then remains substantiallyconstant during the final or steady-state portion of theelectrotherapeutic phase. The steady-state value of the impedance anglesof impedance-angle/time relations 606A and 606B, however, differ fromone another. Impedance-angle/time relation 606A indicates a steady-statevalue of impedance angle θ_(A) that is smaller than the steady-statevalue of impedance angle θ_(B) indicated by impedance-angle/timerelation 606B.

Such a difference in impedance angles θ_(A) and θ_(B) can be used todetermine presence or absence of a conductive foreign body within tissueengaged by an electrosurgical instrument. For example, a predeterminedthreshold value of impedance angle θ_(THRESH) can be compared with themeasured impedance angle of the biological tissue. If the measuredsteady-state impedance angle is less than the predetermined anglethreshold θ_(THRESH), as it is in impedance-angle/time relation 606A,then absence of a conductive foreign body can be determined. If,however, the measured steady-state impedance angle is greater than thepredetermined angle threshold θ_(THRESH), as it is inimpedance-angle/time relation 606B, then presence of a conductiveforeign body can be determined. In response, a control circuit, such asthe control circuit 48 of FIG. 2, can generate an error notificationthat indicates a presence of a conductive foreign body in the engagedbiological tissue and reduce or terminate delivery of the therapeuticsignal. However, if a similar impedance is identified without a steadystate impedance angle greater than the predetermined threshold, than thecontrol circuit can continue to allow delivery of the therapeuticsignal. Energy can be applied and increased until boiling is detected.As resistance is low in this state, current would be at the high end ofits typical value until boiling starts.

In some examples, impedance or resistance of the engaged biologicaltissue is measured during an interrogation phase. If the magnitude ofthe measured impedance or resistance of the engaged biological tissue isless than a predetermined resistance value, then the phase angle of theimpedance will be determined and compared with the predeterminedthreshold θ_(THRESH).

In some examples, if the measured steady-state impedance angle is lessthan the predetermined angle threshold θ_(THRESH), as it is inimpedance-angle/time relation 606A, then an open circuit can bedetermined. In response, the control circuit can generate an errornotification that indicates an open circuit and can reduce or terminatethe delivery of the therapeutic signal. In some examples, in response tothe measured reference impedance angle being greater than a first angle,e.g., angle θ_(A), and less than a second angle, e.g., angle θ_(B), thecontrol circuit can reduce a power level of the therapeutic signal. Insome examples, the first angle can be about 70 degrees, which can bedevice dependent.

In this manner, the system can compare the measured reference impedanceangle with the predetermined angle threshold θ_(THRESH) and generate aresponse indicative of an environmental condition of the instrumentbased on the comparison of the measured reference impedance angle withthe angle threshold. The response can include a reduction in powerand/or produce a signal indicative of the environmental condition. Theresponse can include a notification signal, such as to indicate thecondition to the user.

FIG. 13 is a flow chart of a method for determining presence or absenceof a metal object in biological tissue engaged by an electrosurgicalinstrument. In FIG. 13, method 620 begins at step 622, in whichbiological tissue is engaged by an electrosurgical instrument. Then, atstep 624, control circuit 48 (depicted in FIG. 2) causeselectrical-energy source 44 (depicted in FIG. 2) to provide anelectrotherapeutic signal to the engaged biological tissue during anelectrotherapeutic phase. Then, at step 626, the elapsed therapy time Tis compared with a predetermined time threshold T_(MEASURE) at whichtime steady-state tissue impedance has been reached. If, at step 626,elapsed therapy time T is less than time threshold T_(MEASURE), thenmethod 620 returns to step 624 where the electrotherapeutic schedulecontinues.

If, however, at step 626, elapsed therapy time T is greater than timethreshold T_(MEASURE), then method 620 advances to step 628 wherecontrol circuit 48 causes measurement circuit 46 (depicted in FIG. 2) tomeasure impedance angle θ_(MEAS) of the engaged biological tissue. Then,at step 630, the measured impedance angle θ_(MEAS) of the engagedbiological tissue is compared to a predetermined reference angleθ_(REF). If, at step 630, the measured impedance angle θ_(MEAS) isgreater than the predetermined reference angle θ_(REF), then the controlcircuit can generate an error notification and the method 620 advancesto step 632 where therapy is terminated. For example, the controlcircuit can generate an error notification that indicates a presence ofa conductive foreign body in the engaged biological tissue.

In some examples, a predetermined range of reference angles (e.g.,θ_(MIN)<θ_(MEAS)<θ_(MAX)) can be used to determine whether a conductiveforeign body is engaged by the electrosurgical instrument. If, however,at step 630, the measured impedance angle θ_(MEAS) is less than thepredetermined reference angle θ_(REF), then method 620 advances to step634, where therapy is continued.

The predetermined impedance angle that defines the border separatingpresence and absence of a conductive foreign body can vary depending onthe particular electrosurgical instrument, the electrical parameters ofthe particular electrosurgical signal, the type of biological tissue,etc. For example, the frequency of the electrosurgical signal can berelated to the impedance angle defining the presence/absence threshold.

Short Circuit Error Trapping with Band Between Trigger and Escape Values(FIG. 14)

As described above, the electrosurgical generator, e.g., theelectrosurgical generator 12 of FIG. 2, can coagulate or seal vessels orotherwise modify tissues through the application of electrical energyvia electrotherapeutic signals. One of the problems with such energyapplication is that if electrodes coupled to or integrated with theelectrosurgical instrument become shorted, the electrical energy passespredominately through the shorted area rather than through the tissuesurrounding the shorted area. In such a case, the tissue is largelyunaffected by the application of the electrical energy.

In one approach, insulated standoffs can be used to prevent opposingelectrodes from contacting one another and energy being diverted througha contact point instead of through the tissue. However, electricallyconductive elements can be found in surgery that, when grasped by theelectrosurgical instrument, can result in a similar undesirablechanneling of the energy. Examples of such elements include othersurgical tools, metal clips, and staples.

In some systems, the electrosurgical generator can monitor for aspecific (low) electrical impedance (referred to collectively asimpedance) and can inform the user, e.g., surgeon or technician, thatsuch undesired channeling of energy is currently occurring. If theelectrosurgical generator determines such a low electrical impedance ispresent, the electrosurgical generator can start a timer and alert theuser of the issue via audible and/or visual notifications, for example.

The electrosurgical generator can include a delay prior to anynotification of an occurrence of low impedance to prevent otherincidences of similar low impedances from falsely signaling a “trueshort circuit” incidence. Other incidences of low impedances can occurdue to, for example, saline added at the surgical site, highlyelectrically conductive secretions (such as Gall bladder bile) or thin,moist tissue, such as abdominal omentum surrounding the kidney,especially when used with large electrical surface contact areaelectrodes.

When such environments are encountered, an extended application ofenergy can raise their electrical impedances by driving out fluid orconverting fluids into gases through phase change. This is usuallyachieved within a set period of time, or the user is advised to dry thetip of the electrosurgical instrument and/or grasp the tissue in analternative area, for example. Hence, it is preferable to gain anintended modified tissue by continuing to apply energy during thisinitial short condition when the cause is tissue derived and not aforeign object.

During the application of energy during a tissue-derived initial shortcircuit condition, a fluctuation in the impedance can occur in which theimpedance increases sufficiently to exceed a short circuit trigger valuebut is still in a situation where the low impedance environment cannotbe overcome by the power applied. In this situation, in place of afairly rapid short circuit error, such as around three seconds, theenergy can be applied until other times are reached such as no tissueeffect or maximum activation time errors are met. However, this canextend the procedure, which can frustrate the user and create a negativeuser experience. Applying a filter to this situation can only do so muchas a more positive indicator of driving out of the low impedanceenvironment is more valuable.

The present inventors have recognized the desirability of providing asystem having an improved indication of whether a low impedanceenvironment short has been overcome or whether small increases (followedby decreases) in the environmental impedance has been achieved. Theseimprovements can be particularly desirable in some systems, such assystems where the ability to measure and act upon the impedance feedbackis less accurate. For example, a system can suffer from inaccuracy as aresult of its inability to attain accurate impedance readings due to thelow voltage applied during low impedance situations, which can result ingreater difficulty in detecting phase angle shift caused by the system'sinherent inductive nature as well as the inductance created by thematerial between the devices jaws.

The present inventors have recognized that a two-boundary threshold canbe used to provide an improved indication of whether a low impedanceenvironment short has been overcome or whether small increases (followedby decreases) in the impedance has been achieved. As described in moredetail below, the system can monitor for two impedance values: a triggervalue and an escape value. The system can use a first impedance value (a“trigger” value) to trigger a short circuit and the system can use asecond impedance value (an “escape” value) greater than the firstimpedance value to exit an error clock timing routine.

The present inventors have recognized that a clinician can be locallyboiling fluid, which can create bubbles that have an impedance. At thispoint, there is an apparent increase in the impedance that can push theimpedance reading above the first impedance value but not necessarilyout of a short circuit condition. The present inventors have recognizedthat a second impedance value can be important because it ensures thatthe system is drying out the tissue during a waiting time. By using thetwo-boundary threshold techniques of this disclosure, a short circuitcondition can be quickly communicated to the user, thereby allowing theprocedure to continue more quickly than using other techniques.

FIG. 2, described above, depicts an example of a surgical system thatcan be used to implement various aspects of the two-boundary thresholdtechniques of this disclosure. As shown in FIG. 1, the surgical systemof FIG. 1 can include an electrosurgical device such as the forceps 14.The forceps 14 can include two jaws, e.g., the first jaw member 36 andthe second jaw member 38. In some examples, one of the two jaws can bemoveable, and the other jaw can be stationary. In other examples, bothjaws can be moveable.

It should be noted that the two-boundary threshold techniques of thisdisclosure are not limited to electrosurgical devices that include jaws.Rather, the two-boundary threshold techniques can be implemented usingdevices such as spatulas and snares.

The electrosurgical device, e.g., the forceps 14, can include two ormore electrodes sized, shaped, and/or otherwise configured to deliverthe electrotherapeutic signal to the biological tissue, e.g., the tissue16 of FIG. 1. In some examples, the electrodes can be integral with thejaws, e.g., the first jaw member 36 and the second jaw member 38, as inFIG. 1. In other examples, the electrodes can be coupled to the jaws.

An output circuit, such as including the power source 44 of FIG. 2, canbe configured to generate and deliver electrosurgical energy to anoutput terminal, e.g., the instrument interface 42 of FIG. 2, fordelivery to a patient. The output terminal can be configured to coupleto an electrosurgical device, such as the forceps 14 of FIG. 1, anddeliver electrosurgical energy, e.g., high frequency, such as RF energy,to biological tissue vie electrotherapeutic signals.

A control circuit of the surgical system, e.g., the control circuit 48of the surgical system of FIG. 1, can be coupled to the output circuitand the control circuit can be configured to perform various aspects ofthe two-boundary threshold techniques. For example, a user, such as asurgeon or clinician, can initiate ongoing delivery of electrosurgicalenergy to the biological tissue of a patient, such as tissue positionedbetween two jaws of the electrosurgical device. In some examples, aprocessor, e.g., the processor 54 of the control circuit 48 of FIG. 2,can control a measurement circuit, e.g., the measurement circuit 46 ofFIG. 2, to measure a first impedance value of the tissue in conducivecommunication with the two electrodes of the electrosurgical device,e.g., the forceps 14 of FIG. 1. In some examples, the tissue can bepositioned between two electrodes of the electrosurgical device

The processor can compare the first measured impedance value of thetissue to a first threshold value, e.g., the trigger value. In anon-limiting example for purposes of illustration, the trigger value canbe about 5 ohms. When the first measured impedance value is less than orequal to the first threshold value, the processor e.g., the processor 54of the control circuit 48 of FIG. 2, can initiate a short circuit timer,such as included in the processor. In a non-limiting example forpurposes of illustration, a time limit of the timer can be about 3,000milliseconds (ms) to about 6,000 ms.

The processor can control the measurement circuit to measure a secondimpedance value of the tissue positioned between the two electrodes ofthe electrosurgical device. Then, the processor can compare the secondmeasured impedance value of the tissue to a second threshold value,e.g., the escape value, where the second threshold value (the escapevalue) is greater than the first threshold value (the trigger value). Ina non-limiting example for purposes of illustration, the escape valuecan be about 10 ohms.

The trigger and escape values are representative of typical values butare not absolute and can depend on many factors, such as the impedancewithin the device, the exposed contact area, the ability of theprocessor to measure from feedback the impedance values, and the cablelength of the attached device, among other factors. The trigger andescape values can be tuned or adjusted for various systems. In addition,the value of the timer limit can be tuned or adjusted and can depend ona manufacturer's understanding of surgeon perception and willingness towait to see if a short error will be indicated or a longer period ofpower application (waiting) is preferred.

When the second measured impedance value is less than the secondthreshold value and the timer has not met the time limit, the surgicalsystem can continue the delivery of electrosurgical energy. However,when the second measured impedance value is less than the secondthreshold value and the timer has met the time limit, the controlcircuit can control the output circuit to reduce or terminate thedelivery of electrosurgical energy. In some examples, the controlcircuit can increase the power or current limit or both for a shortperiod of time to continue the delivery of energy to overcome the wetenvironment. In some examples, when the timer has met the time limit,the surgical system can generate an indication to a user. For example, auser interface, e.g., the user interface 50 of the surgical system ofFIG. 2, can generate one or both of an audible indication and a visualindication to the user to indicate that the delivery of theelectrosurgical energy has been reduced or terminated.

The delivery of energy can occur during an interrogation phase in whichthe amount of energy delivered is low, but not zero. For example, duringan interrogation phase, the energy delivered is not sufficient to effecttissue.

In some examples, the control circuit can be configured to adjust atleast one of the first threshold value (the trigger value), the secondthreshold value (the escape value), and the time limit based on at leastone characteristic of the electrosurgical device. For example, currentdensity can affect the amount of power of the deliveredelectrotherapeutic signal, which can affect the amount of energy thesystem delivers to the biological tissue. As an example, the surfacearea of the electrodes of the electrosurgical device can affect thecurrent density. For example, for an electrosurgical device having alarge surface area and a low power electrosurgical generator, there canbe insufficient current to quickly burn off liquids in the tissue. Assuch, it can be desirable for the system to wait for a longer period oftime before reducing or terminating the delivery of energy to thetissue. To that end, the control circuit can adjust at least one of thefirst threshold value (the trigger value), the second threshold value(the escape value), and the time limit using the surface area of theelectrode(s). For example, the control circuit can retrieve various oneor more parameters of the electrosurgical device stored in a memorydevice, where the one or more parameters can include the surface area ofthe electrode(s) associated with the electrosurgical device.

In addition, a jaw force of the electrosurgical device can affect thecurrent density. For example, a stronger jaw force can increase theamount of tissue in contact with the electrodes, which can affect theboiling point of the tissue. As such, the control circuit can adjust atleast one of the first threshold value (the trigger value), the secondthreshold value (the escape value), and the time limit forelectrosurgical devices with a greater jaw force. An electrosurgicaldevice, such as the forceps 14 of FIG. 1, can include a jaw force sensorconfigured to sense a jaw force, where the jaw force sensor is incommunication with a control circuit, such the control circuit 48 ofFIG. 2.

In addition to characteristics of the electrosurgical device, at leastone of the first threshold value (the trigger value), the secondthreshold value (the escape value), and the time limit can be proceduredependent. For example, some procedures and/or tissues are more wet thanothers. As an example, hepatic procedures can involve significant bloodfrom the liver. In some procedures, the clinician can introducesignificant fluid to clean tissue. As such, it can be desirable duringsome procedures for the system to wait for a longer period of timebefore terminating the delivery of energy to the tissue. To that end, insome examples, the control circuit can adjust at least one of the firstthreshold value (the trigger value), the second threshold value (theescape value), and the time limit to allow the electrosurgical generatoradditional time to burn off excess fluid, if needed.

Alternatively, or in addition to, the characteristic(s) of theelectrosurgical device can be used to adjust the threshold values ortime limit. For example, the output current of the electrosurgicalgenerator can affect the amount of power of the deliveredelectrotherapeutic signal, which can affect the amount of energy thesystem delivers to the biological tissue. In some examples, based on theoutput current, for example, the control circuit can adjust at least oneof the first threshold value (the trigger value), the second thresholdvalue (the escape value), and the time limit to allow theelectrosurgical generator additional time to burn off excess fluid, ifneeded.

In some examples, the two-boundary threshold techniques of thisdisclosure can be used during an initial tissue interrogation phase atthe beginning of the procedure. In other examples, the techniques can beused partway through the procedure, such as during the heating or dryingphases.

For purposes of explanation, non-limiting examples of a system with andwithout the escape value will now be described. Initially, a cliniciancan press an activation button and energy is attempted to be deliveredto electrosurgical device, e.g., to the jaw. But, due to the highlyconductive nature of the saline and blood washing over theelectrosurgical device, the electrosurgical generator identifies thatthe impedance is 4 ohms and a short circuit timer begins.

For a system without an escape value, the electrosurgical generator canprovide energy and at 1,000 ms of applied energy time, through the shortcircuit timer, a bubble is created, e.g., at the device jaw, whichincreases the impedance to 6 ohms. The bubble is transitionary, butbecause the impedance is now above a 5-ohm threshold, the short circuittimer is reset and the electrosurgical generator starts its 3,000 mscountdown again.

The transitionary bubble can appear a number of times, but it can beknocked away from the jaw again and again, resetting the short circuittimer each time, until eventually another alarm, such as an extendedactivation time alarm, is triggered, such as between about 12,000 ms toabout 30,000 ms. The clinician can become frustrated by this experienceand realize that they have to extract some of the surrounding saline orgrasp the tissue differently to achieve a good seal.

For a system without an escape value, as described above, theelectrosurgical generator can provide energy and at 1,000 ms of appliedenergy time, through the short circuit timer, a bubble is created, e.g.,at the device jaw, which can increase the impedance to 6 ohms. However,because an escape value, e.g., 10 ohms, is needed to exit the shortcircuit loop, the short circuit timer continues. Another bubble iscreated that can again increase the impedance to 6 ohms, which is againignored by the short circuit timer because the impedance has not met theescape value, or the upper boundary requirement. At 3,000 ms the shortcircuit alarm is presented to the clinician and the clinician now knowsthat either the fluid must be removed, or the tissue grasped in adifferent way. This reaction is much quicker due to the upper boundary“escape” value of the 10 ohms, allowing the procedure to continue morequickly.

The two-boundary threshold techniques described above can also beincorporated into other systems that utilize short circuit triggers. Forexample, if the trigger value is met, then the system, while waiting tosee if the short circuit timer or the escape value will be met first,can also interrogate the feedback to determine and interpret the phaseangle at that point in time. If the phase angle is above a particularthreshold, then the system can determine that the frequency of phaseangle, coupled with the low impedance, indicates that a metal object isinadvertently (or otherwise) grasped by the electrosurgical device. Thesystem can continue monitoring the phase angle until the upper escapevalue has met or the short circuit timer, e.g., 3,000 ms, is met.

FIG. 14 is a flow diagram depicting an example of the two-boundarytechnique described above. At block 1000, a processor, e.g., theprocessor 54 of the control circuit 48 of FIG. 2, can determine whethera short circuit flag is set. If the short circuit flag is not set (“NO”branch of block 1000), the processor can compare a measured impedance toa first impedance threshold, e.g., a 5-ohm threshold, at decision block1002.

If the processor determines that the impedance is less than the firstthreshold (“YES” branch of block 1002), then the processor resets theshort circuit timer and sets the short circuit flag at block 1004 andsealing can resume at block 1006. If the processor determines that theimpedance is not less than the first threshold (“NO” branch of block1002), then the processor resets the short circuit timer and removes theshort circuit flag at block 1008 and sealing can resume at block 1006.

However, if the short circuit flag is set (“YES” branch of block 1000),the processor can compare a measured impedance to a second impedancethreshold, e.g., a 7-ohm threshold, at decision block 1010. If theprocessor determines that the impedance is not less than the secondthreshold (“NO” branch of block 1010), then the processor resets theshort circuit timer and resets the short circuit flag at block 1008 andsealing can resume at block 1006. If the processor determines that theimpedance is less than the second threshold (“YES” branch of block1010), then the processor can compare the short circuit timer to a timerlimit, e.g., 3000 ms, at block 1012.

If the processor determines that the short circuit timer is greater thanthe timer limit (“YES” branch of block 1012), then the processor cangenerate a short circuit alert, e.g., audible and/or visualnotification, to notify the user at block 1014. If the processordetermines that the short circuit timer is not greater than the timerlimit (“NO” branch of block 1012), then sealing can resume at block1006.

In this manner, if the impedance is less than the first impedancethreshold, e.g., 5 ohms, consistently for a duration of at least thatdefined by the short circuit timer, e.g., 3000 ms, a short-circuit alertcan be generated and the electrotherapeutic signal will be reduced orterminated. There can be a hysteresis between the first and secondimpedance thresholds, e.g., 5 ohms and 7 ohms, such that a timer, e.g.,having a 3000 ms timer limit, will be started when the impedance fallsbelow the first threshold, e.g., 5 ohms, and reset when the measuredimpedance rises above the second threshold, e.g., 7 ohms.

Open Circuit Check for Impedance Limit Endpoint Waveform (FIGS. 15 and16)

RF vessel sealing devices often use either a fixed maximum impedancevalue, such as to indicate that the tissue is appropriately affected, oran impedance delta to detect when the tissue has been adequatelyaffected. Impedance can also be used to identify if the device jaws havebeen opened during activation. For example, the system can attempt todetect an impedance above a set point to identify an “open circuit,”which signifies that the jaws are open.

In some cases, however, opening the jaws during activation can result ina “false positive” in which the generator signals a good seal but, inreality, the user has just opened the device jaws. For example, with thesystem monitoring for a “good seal” end point, e.g., of 350 ohms, and an“open circuit” error value, e.g., of 2000 ohms, the system can react inthis false positive way during activation. The user controls applicationof energy to the tissue and the system can monitor for both the endpointand the open circuit. In a correct activation, the energy applicationcan initially lower the impedance, e.g., from 30 ohms to 15 ohms, andthen can raise the impedance of the tissue as the energy dries out thetissue. The energy rise can meet the endpoint value of 350 ohms and thegenerator can stop applying power and send a signal to the userindicating that the seal is complete.

In another example, the user controls application of energy to tissueand the energy application can initially lower the impedance of thetissue, e.g., from 30 ohms to 15 ohms, and then the impedance starts torise. During this rise period, the user slowly (or rapidly) opens thejaws. The impedance value can increase rapidly, passing first throughthe required 350-ohm boundary, at which time the system turns off thepower and reports a good seal. Because the energy is turned off (andcontinued energy application can create a “sticky tissue to jaw”situation if a greater than 350-ohm tissue situation is created) and theimpedance will not reach the “open circuit” error value of 2000 ohms,the system erroneously reports a good seal.

The present inventors have recognized the need to include an opencircuit check that begins with initiating a timer when a user initiatesan ongoing delivery of electrosurgical energy to biological tissue. Whenthe timer reaches a timer limit (or “times out”), the system candetermine the impedance value and determine if the impedance valuerepresents an open circuit. If the impedance value does represent anopen circuit, the system can reduce or terminate delivery of energy and,if not, the system can allow continued application of energy until theimpedance meets an endpoint value.

Using the proposed timer techniques, an electrosurgical generator, e.g.,electrosurgical generator 12 of FIG. 2, can apply energy to the systemand to biological tissue in contact with an electrosurgical device, suchbetween the jaws of the forceps 14 of FIG. 1. A processor, e.g., theprocessor 54 of the control circuit 48 of FIG. 2, system can set atimer, e.g., 50-100 ms, when the control circuit has determined that thetissue is ready to be driven to a final impedance end point value orimpedance delta value.

When the timer “times out”, a measurement circuit, e.g., the measurementcircuit 46 of FIG. 2, to measure an impedance value. The processor candetermine whether the measured impedance represents an open circuit andenergy delivery should be reduced or terminated, or whether the measuredimpedance is below an open circuit value and energy delivery cancontinue until the impedance meets the required endpoint value. By usingthese techniques, there is a minimum period of time in which neither theendpoint value nor an open circuit value can be achieved but dependingon the impedance measured at the end of this period, the processor candecide whether to flag an “open circuit” error and reduce or terminatedelivery of energy or continue delivering energy to the complete sealcycle endpoint impedance value.

Several possible scenarios will now be described that can occur usingthe open circuit check techniques. In a first scenario, the user appliesenergy to the tissue, e.g., between the jaws of the electrosurgicaldevice, and the impedance of the tissue decreases and then increases.The processor can recognize that the tissue is suitably affected and canthen start the timer. After a time limit, e.g., 50 ms, the impedance isbelow the “open circuit” value, e.g., an absolute value of 2000 ohms oran impedance delta value, but is also below the target tissue endpointvalue (or an impedance delta value). As such, the processor continues tocontrol the application of power until the target endpoint value isachieved. The processor terminates application of power and indicates tothe user that a good seal has been achieved.

In some examples, a rate of change of impedance can be a triggeringvariable. For example, if the impedance rate of change exceeds a presetvalue, the generator can report an open circuit and then modify theenergy output (or terminate or significantly reduce).

In a second scenario, the user applies energy to the tissue, e.g.,between the jaws of the electrosurgical device, and the impedance of thetissue decreases and then increases. The processor can recognize thatthe tissue is suitably affected and can start the timer. After a timelimit, e.g., 50 ms, the impedance is below the “open circuit” value,e.g., an absolute value of 2000 ohms or an impedance delta value, butthe tissue is at or greater than the tissue endpoint value, e.g., 350ohms. The processor terminates application of power and indicates to theuser that a good seal has been achieved.

In a third scenario, the user applies energy to the tissue, e.g.,between the jaws of the electrosurgical device, and the impedance of thetissue decreases and then increases.

The processor can recognize that the tissue is suitably affected and canthen start the timer. The user releases the tissue prematurely, e.g., byopening the device jaws, and the impedance increases rapidly through theendpoint value, then through the open circuit value, e.g., an absolutevalue of 2000 ohms or an impedance delta value. After 50 ms, forexample, the processor can determine that the impedance is in excess ofthe open circuit value, terminate application of power, and indicate anincomplete seal “open circuit” error message to the user.

The duration of the timer can be important to the success of correctlyidentifying an open circuit and a good seal. If the duration is toolong, small amounts of tissue can rapidly reach impedance values greaterthan the open circuit value, such as when the user is attempting toaffect thin fascia material on the internal wall of the pelvic cavity.Although such tissue is typically initially very electricallyconductive, the fluid content can rapidly boil and the impedance of aportion of such thin material, e.g., within the device jaws, leads to arapidly rising impedance. If the timer duration is 200 ms, for example,a good seal or tissue modification of a thin fascia material on theinternal wall of the pelvic cavity, would lead to an error message,rather than an appropriate good seal tone.

If the timer is too short, a false positive is possible. For example, ifthe timer is set to 10 ms, then the following scenario can occur. Theuser applies energy to tissue and the impedance decreases and thenincreases. As the impedance increases, the processor determines that thetissue is ready to be driven to the endpoint and starts the timer. Ifthe jaws are opened slowly, an impedance ramp rate of the jaws does notmeet the open circuit value within the 10 ms and therefore the controlcircuit continues applying energy. As the impedance continues toward theopen circuit value of 2000 ohms, for example, the impedance value passesthrough the 350-ohm endpoint value and stops applying power, incorrectlygiving a good seal tone at the end.

The value of the timer, the endpoint impedance, and the open circuitimpedance can depend on a number of factors such as the following (aloneor in combination): 1) the amount of power being applied to the tissueat the time (and may be either a set power or a power that takes intoconsideration the power and adjusts the timer and or the impedancevalues accordingly); 2) the target tissue (prior power feedback canprovide an indication of the type of tissue between the jaw and predictthe likely or expected impedance ramp rate and adjust the timer and orthe impedance value accordingly; and 3) the surface area of theelectrodes and or the force that the electrode jaws apply in their fullyclosed position.

Using the open circuit check techniques described in more detail below,the electrosurgical system, e.g., the system 10 in FIG. 2, can set atimer, e.g., 50 ms-100 ms, when the tissue is ready to be driven to anendpoint value (of a seal). When the timer reaches a limit and “timesout”, the system can measure the impedance (or a rate of change withrespect to time of impedance) and determine whether the value representsan open circuit condition or whether to allow continued application ofenergy until the impedance meets the endpoint value, which indicates agood seal. In this way, there is a minimum period of time in whichneither the endpoint value nor an open circuit value can be achieved.But, depending on the impedance determined at the end of the timer, thesystem can determine whether to continue to a complete seal cycleendpoint value or indicate that an open circuit is present.

FIG. 15 is a flow diagram depicting an example of the open circuit checktechniques described above that can be used in a surgical system. Asshown in FIG. 1, the surgical system of FIG. 1 can include anelectrosurgical device such as the forceps 14. The forceps 14 caninclude two jaws, e.g., the first jaw member 36 and the second jawmember 38. In some examples, one of the two jaws can be moveable and theother jaw can be stationary. In other examples, both jaws can bemoveable.

It should be noted that the open circuit check techniques of thisdisclosure are not limited to electrosurgical devices that include jaws.Rather, the open circuit techniques can be implemented using devicessuch as spatulas and snares.

The electrosurgical device, e.g., the forceps 14, can include two ormore electrodes sized, shaped, and/or otherwise configured to deliverthe electrotherapeutic signal to the biological tissue, e.g., the tissue16 of FIG. 1. In some examples, the electrodes can be integral with thejaws, e.g., the first jaw member 36 and the second jaw member 38, as inFIG. 1. In other examples, the electrodes can be coupled to the jaws.

An output circuit, such as including the power source 44 of FIG. 2, canbe configured to generate and deliver electrosurgical energy to anoutput terminal, e.g., the instrument interface 42 of FIG. 2, fordelivery to a patient. The output terminal can be configured to coupleto an electrosurgical device, such as the forceps 14 of FIG. 1, anddeliver electrosurgical energy, e.g., high frequency, such as RF energy,to biological tissue vie electrotherapeutic signals. A control circuitof the surgical system, e.g., the control circuit 48 of the surgicalsystem of FIG. 1, can be coupled to the output circuit and the controlcircuit can be configured to perform various aspects of the open circuitcheck techniques.

Referring now to FIG. 15, at block 1100, the control circuit caninitiate a timer when a user, such as a surgeon or clinician, initiatesan ongoing delivery of electrosurgical energy to biological tissuepositioned between two electrodes of the electrosurgical device. In someexamples, the timer can be included in the processor, such as in theprocessor 54 in FIG. 2. In some examples, the control circuit can setthe timer when the control circuit has determined that the tissue isready to be driven to a final impedance end point value (or impedancedelta value). In some examples, a processor, e.g., the processor 54 ofthe control circuit 48 of FIG. 2, can control a measurement circuit,e.g., the measurement circuit 46 of FIG. 2, to measure an impedancevalue of the tissue positioned between two electrodes of theelectrosurgical device, e.g., the forceps 14 of FIG. 1.

At block 1102, the processor can determine whether the timer is greaterthan the timer limit, e.g., 50 ms-100 ms. If the timer has not exceededthe time limit (“NO” branch of block 1102), then system can continue thedelivery of electrosurgical energy at block 1104. If the timer has metthe time limit (“YES” branch of block 1102), then the processor cancompare a representation of the measured impedance to a first thresholdvalue (the endpoint value), e.g., 250-350 ohms, at block 1106. The firstthreshold value can be stored in memory, such as in memory 56 in FIG. 2.

At block 1108, if the processor determines that the representation ofthe measured impedance is less than the first threshold value (“YES”branch of block 1108) (the endpoint value), then the processor cancontinue the delivery of electrosurgical energy. If the processordetermines that the representation of the measured impedance is not lessthan the first threshold value (“NO” branch of block 1108), then theprocessor can compare a representation of the measured impedance to asecond threshold value (the open circuit value), e.g., 2000 ohms, atblock 1110. The second threshold value can be stored in memory, such asin memory 56 in FIG. 2.

If the processor determines that the representation of the measuredimpedance is less than the second threshold value (“YES” branch of block1110), then the processor can reduce or terminate the delivery ofelectrosurgical energy at block 1112. Here, the measured impedance isgreater than the first threshold value (the endpoint value) and lessthan the second threshold value (the open circuit value), whichindicates that a good seal has been achieved. In some examples, thecontrol circuit can generate a notification to the user to indicate agood seal.

If the processor determines that the representation of the measuredimpedance is not less than the second threshold value (“NO” branch ofblock 1110), then the processor can reduce or terminate the delivery ofelectrosurgical energy at block 1114. Here, the measured impedance isgreater than the first threshold value (the endpoint value) and alsoequal to or greater than the second threshold value (the open circuitvalue), which indicates that there is an open circuit. In some examples,the surgical system can generate an indication to the user to indicatean open circuit. For example, a user interface, e.g., the user interface50 of the surgical system of FIG. 2, can generate one or both of anaudible indication and a visual indication to the user to indicate thatthe delivery of the electrosurgical energy has been reduced orterminated and an open circuit was detected.

As indicated above, in some examples a processor, e.g., the processor 54of the control circuit 48 of FIG. 2, can control a measurement circuit,e.g., the measurement circuit 46 of FIG. 2, to measure the impedancevalue of the tissue and the processor can determine whether arepresentation of the measured impedance exceeds a threshold value. Insome examples, the representation of impedance includes a value of theimpedance, such as an absolute value of impedance. In other examples,the representation of impedance includes a change with respect to timein the value of the impedance (or “delta”), such as a first derivativeof impedance with respect to time.

FIG. 5 is a flow diagram depicting another example of the open circuitcheck techniques described above that can be used in a surgical system.In the method 300, at block 302, the control circuit can initiate atimer at the beginning of Phase 3. At block 304, the control circuit canapply electrosurgical energy to biological tissue positioned between twoelectrodes of the electrosurgical device. At block 306, the controlcircuit can determine whether an endpoint is met. If the control circuitdetermines that an endpoint has not been met (“NO” branch of block 306),then the control circuit can return to block 304 and continue to applyelectrosurgical energy to the biological tissue. However, if the controlcircuit determines that an endpoint has been met (“YES” branch of block306), then the method proceeds to block 308.

At block 308, the control circuit can determine whether an elapsed timeis less than or equal to a timer limit. If the control circuitdetermines that the elapsed time is less than or equal to a timer limit(“YES” branch of block 308), then the control circuit can reduce thedelivery of electrosurgical energy and indicate an open circuit at block310. If the control circuit determines that the elapsed time is not lessthan or equal to a timer limit (“NO” branch of block 308), then thecontrol circuit can reduce the delivery of electrosurgical energy andindicate a good seal is present at block 312.

FIG. 16 is a flow diagram depicting another example of the open circuitcheck techniques described above that can be used in a surgical system.FIG. 16 is similar to FIG. 15 except that in FIG. 16 the control circuitcan compare a rate of change of impedance with respect to time of thebiological tissue, e.g., 40 kiloohms per second, to a threshold value.

Referring now to FIG. 16, at block 1200, the control circuit caninitiate a timer in response to a delivery of electrosurgical energy tobiological tissue positioned between two electrodes of theelectrosurgical device. In some examples, the timer can be included inthe processor, such as in the processor 54 in FIG. 2. In some examples,the control circuit can set the timer when the control circuit hasdetermined that the tissue is ready to be driven to a final impedanceend point value (or impedance delta value). In some examples, aprocessor, e.g., the processor 54 of the control circuit 48 of FIG. 2,can control a measurement circuit, e.g., the measurement circuit 46 ofFIG. 2, to measure an impedance value of the tissue positioned betweentwo electrodes of the electrosurgical device, e.g., the forceps 14 ofFIG. 1.

At block 1202, the processor can determine whether the timer is greaterthan the timer limit, e.g., 50 ms-100 ms. If the timer has not exceededthe time limit (“NO” branch of block 1202), then system can continue thedelivery of electrosurgical energy at block 1204. If the timer has metthe time limit (“YES” branch of block 1202), then the processor cancompare a rate of change with respect to time of the measured impedanceto a first threshold value (the endpoint value) at block 1206. The firstthreshold value can be stored in memory, such as in memory 56 in FIG. 2.A non-limiting example of a rate can be 2000 ohms over a time period of50 ms, or 40,000 ohms/s.

At block 1208, if the processor determines that the rate of change ofthe measured impedance is less than the first threshold value (“YES”branch of block 1208)(the endpoint value), then the processor cancontinue the delivery of electrosurgical energy at block 1204. If theprocessor determines that the rate of change of the measured impedanceis not less than the first threshold value (“NO” branch of block 1208),then the processor can compare the rate of change of the measuredimpedance to a second threshold value (the open circuit value) at block1210. The second threshold value can be stored in memory, such as inmemory 56 in FIG. 2.

If the processor determines that the rate of change of the measuredimpedance is less than the second threshold value (“YES” branch of block1210), then the processor can reduce or terminate the delivery ofelectrosurgical energy at block 1212. Here, the rate of change isgreater than the first threshold value (the endpoint value) and lessthan the second threshold value (the open circuit value), whichindicates that a good seal has been achieved. In some examples, thecontrol circuit can generate a notification to the user to indicate agood seal.

If the processor determines that the rate of change of the measuredimpedance is not less than the second threshold value (“NO” branch ofblock 1210), then the processor can reduce or terminate the delivery ofelectrosurgical energy at block 1214. Here, the rate of change isgreater than the first threshold value (the endpoint value) and alsoequal to or greater than the second threshold value (the open circuitvalue), which indicates that there is an open circuit. In some examples,the surgical system can generate an indication to the user to indicatean open circuit. For example, a user interface, e.g., the user interface50 of the surgical system of FIG. 2, can generate one or both of anaudible indication and a visual indication to the user to indicate thatthe delivery of the electrosurgical energy has been terminated and anopen circuit was detected.

By using the open circuit check techniques described above, the systemcan provide fewer erroneous good seal indications.

Alternate Power Correction Outputs in Low Accuracy Hardware Systems(FIG. 17)

Electrosurgical generators are constantly evolving with new “state ofthe art” hardware that allows the generators to be ever more accurateand responsive to the feedback from the tissues that they intend tomodify. The improvement in hardware architecture can provide manybenefits over their less advanced or historical counterparts, such asproviding greater CPU speed, which can allow faster responses incollecting, analyzing, and reacting to data, as well as newfunctionality that permit phase angle calculations, for example, whichcan provide more accurate indications of feedback-based derived datasuch as power delivery, impedance, etc.

There is often a desire to gain the performance of new “state of theart” hardware with existing hardware that is already placed in thehospital, providing the same performance to the user with this olderplaced capital equipment rather than having to update to new capitalequipment. Such performance improvements can be important in someelectrosurgical applications to ensure the best possible tissuemodification performance for the patient.

For example, appropriate power delivery can be important in providingoptimal tissue performance in vessel sealing. Too much energy deliveredtoo quickly can result in tissue damage from steam pockets within thetissue. Slow application of energy can significantly extend proceduretimes and result in longer periods in which the patient is underanesthesia, which can result in reduced benefits of surgical outcomesand higher risk of patient recovery issues. From a competitivestandpoint, quick tissue modification with a high level of confidence ofresultant correct tissue effect can be central to having a marketacceptable device.

Many older electrosurgical systems may not have the ability toaccurately measure the phase angle of the RF output. During the sealingprocess, the variation of the tissue grasped between the jaws and itsinteraction with the inherent inductance and capacitance in the outputcircuit can cause phase angle changes in the RF waveform. Calculationsof power and load resistance can be inaccurate if this phase angle isnot considered and therefore measuring this parameter can increase theaccuracy of the system.

When the voltage (“E”) leads the current (“I”), helpfully rememberedwith the mnemonic “ELI”, the load is considered to be inductive. Whenthe current (“I”) leads the voltage (“E”), helpfully remembered with themnemonic “ICE”, the load is considered to be capacitive. In either the“ELI” or “ICE” scenario, the outcome of a phase angle offset is areduction in actual power delivery compared to the apparent powerdelivery that the electrosurgical generator believes it is providing dueto the misalignment of the peaks of the current and voltage.

The accuracy of the voltage applied can further compound the issue. Theaccuracy of voltage application of older systems can become difficult asthe voltage decreases—especially when the voltage has been created tocontrol high rates intended for monopolar outputs, e.g., 4000V orhigher, which are then applied to bipolar outputs that can go as low astens of volts or less. This can result in hardware manufacturerscreating “tuned hardware” that is tuned for accuracy within certainimpedance and voltage ranges within which devices are typically requiredto work, with expected phase shifts. In lower ranges of impedance, theaccuracy of the calculated power delivery can become very difficult dueto voltage levels being so low.

As an example, to supply a specific power, e.g., 100 W, a systemsupplies a current (I) at a voltage (V) to meet the power requirement.The impedance determines the makeup of the voltage and the current todeliver the required power. For example, if the impedance is 5 ohms,then the electrosurgical generator can provide a 4.5 A output at 22.22V.

As another example, if the same system attempts to deliver 30 W (31.25W) into an impedance of 5 ohms, then the electrosurgical generator canprovide approximately a 2.5 A output at 12.5V. Consider this 12.5Voutput on a system set to provide as much as 4000V in some cases. Atypical impedance range for which older electrosurgical systems becomeless accurate is about 0-50 ohms. For such an impedance range, an olderelectrosurgical system can struggle to apply enough current to burn offfluid in the tissue to provide a good seal because the electrosurgicalgenerator's power output is not sufficiently accurate.

The present inventors have recognized the need to improve the powercontrol in legacy electrosurgical systems. To solve this need, thepresent inventors have recognized that applying a power correction atlower impedance values can improve the power control in legacyelectrosurgical systems and overcome their lack of accuracy.

As shown in FIG. 1, the surgical system of FIG. 1 can include anelectrosurgical device such as the forceps 14. The forceps 14 caninclude two jaws, e.g., the first jaw member 36 and the second jawmember 38. In some examples, one of the two jaws can be moveable, andthe other jaw can be stationary. In other examples, both jaws can bemoveable.

It should be noted that the power correction techniques of thisdisclosure are not limited to electrosurgical devices that include jaws.Rather, the power correction techniques can be implemented using devicessuch as spatulas and snares.

The electrosurgical device, e.g., the forceps 14, can include two ormore electrodes sized, shaped, and/or otherwise configured to deliverthe electrotherapeutic signal to the biological tissue, e.g., the tissue16 of FIG. 1. In some examples, the electrodes can be integral with thejaws, e.g., the first jaw member 36 and the second jaw member 38, as inFIG. 1. In other examples, the electrodes can be coupled to the jaws.

An output circuit, such as including the power source 44 of FIG. 2, canbe configured to generate and deliver electrosurgical energy to anoutput terminal, e.g., the instrument interface 42 of FIG. 2, fordelivery to a patient. The output terminal can be configured to coupleto an electrosurgical device, such as the forceps 14 of FIG. 1, anddeliver electrosurgical energy, e.g., high frequency, such as RF energy,to biological tissue vie electrotherapeutic signals. A control circuitof the surgical system, e.g., the control circuit 48 of the surgicalsystem of FIG. 1, can be coupled to the output circuit and the controlcircuit can be configured to perform various aspects of the powercorrection techniques.

FIG. 17 is a flow diagram depicting an example of power correctiontechniques that can be used in a surgical system. At block 1300, ameasurement circuit, e.g., the measurement circuit 46 of FIG. 2, tomeasure a representation of an impedance of the tissue positionedbetween two electrodes of the electrosurgical device, e.g., the forceps14 of FIG. 1. In some examples, the control circuit can measure acentral tendency, such as a mean, median, mode, or other centraltendency, during a portion of the output, such as during the last 50 msof output, and store these values, such as in the memory 56 of FIG. 2.

At block 1302, the control circuit can compare the measuredrepresentation of impedance to a first threshold, e.g., about 50 ohms,stored in memory, such as the memory 56 of FIG. 2. The first threshold,e.g., 50 ohms, can be based on an impedance value below which a powercorrection is needed for an electrosurgical system. The first thresholdcan be adjusted based on the electrosurgical system.

If the impedance is not less than the first threshold (“NO” branch ofblock 1302), then the impedance is high enough that the control circuitdoes not need to apply a power correction to the power control of theelectrosurgical generator, as shown at block 1304. The electrosurgicalsystem can apply power via a normal operation.

However, if the impedance is less than the first threshold (“YES” branchof block 1302), then the control circuit can apply a power correction tothe power control of the electrosurgical generator. For example, asshown at block 1306, the control circuit can determine whether themeasured impedance is within a first range of impedances, e.g., 0-100ohms. If the measured impedance is within the first range of impedances(“YES” branch of block 1306), then the control circuit can select afirst power correction associated with the first range of impedances andapply the selected first power correction at block 1308.

If the measured impedance is not within the first range of impedances(“NO” branch of block 1306), then the control circuit can select asecond power correction associated with a second range of impedance,e.g., 20-100 ohms, when the representation of the impedance is withinthe second range, e.g., 20-100 ohms, and apply the selected second powercorrection at block 1310. As an example, the ‘desired power’ can be 100W, but the system can actually be measuring only 50 W. The correctionfactor can be applied to the measured value to ensure correctcompensation is applied to the output.

The electrosurgical system can apply the power corrections using alinear calculation, such as the following equation:

Corrected Power=(((Zload×A)+B)×MeasuredPower)/1000   Equation (1)

where Zload is the measured impedance of the tissue, A and B arespecific power correction values or parameters that can be selected toprovide different possible power correction trajectories, andMeasuredPower is the power that the electrosurgical system believes itis providing to the tissue (V×I). The processor, e.g., the processor 54of FIG. 2, can retrieve the A and B parameters from memory, e.g., memory56 of FIG. 2, and calculate a corrected power setting using Equation (1)above. In a first non-limiting example for purposes of explanation only,a first calculation of a power correction for 10 ohms can use a value of11 for A and 548 for B. In a second non-limiting example for purposes ofexplanation only, a first calculation of a power correction for 50 ohmscan use a value of 11 for A and 419 for B.

Using the corrected power setting, the control circuit can deliverelectrosurgical energy via the electrodes of the electrosurgical device.In some examples, the control circuit can reduce or terminate theapplication of the selected power correction to the power setting whenthe representation of impedance meets or exceeds a threshold value.Continuing with the example described above, the control circuit caninitially apply a power correction for a measured impedance of 15 ohms,which is below 50 ohms and within the first range of 0-20 ohms, andreduce or terminate the application of that power correction when themeasured impedance exceeds 20 ohms, which is above the upper limit ofthe first range. In some examples, the control circuit can beginapplying a new power correction based on the change in impedance.Continuing with the example described above, for a measured impedance of21 ohms, which is below 50 ohms and within the second range of 20-50ohms, the control circuit can apply a new power correction to the powersetting.

In some examples, rather than having a single impedance value, e.g., 20ohms, be the difference between the first range, e.g., 0-20 ohms, andthe second range, e.g., 20-50 ohms, it can be desirable for the controlcircuit to use hysteresis to prevent the system from oscillating betweentwo power corrections. When implemented, hysteresis can dynamicallychange the threshold limits depending on the present ‘state’ of thesystem, which can prevent unintended oscillation between the at leasttwo thresholds when the measured parameter is near the thresholds. Itcan influence one or both of the upper and lower portions of thethresholds. In this manner, the control circuit can dynamically adjustat least one of an upper limit and a lower limit of the first range whenthe representation of the impedance is within a predetermined percentageor value of the upper or lower limit.

For example, a specified percentage can be used at the boundaries of theranges. As an example, for measured impedances within 20% of the 20 ohmupper limit of the first range, the control circuit can use candynamically adjust, e.g., increase, one or both of the upper and lowerlimits associated with the first range.

In another example, rather than use a percentage for hysteresis, thecontrol circuit can use a specified impedance value at the boundaries ofthe ranges. As an example, for measured impedances within 4 ohms of the20 ohm upper limit of the first range, the control circuit candynamically adjust, e.g., increase, one or both of the upper and lowerlimits associated with the first range.

It should be noted that although two non-limiting examples of rangeswere described with two corresponding power corrections, in someexamples, only one range can provide sufficient power correction. Inother examples, more than two ranges with corresponding powercorrections can be used.

The power correction techniques described above can significantlyimprove the power control of an electrosurgical system to artificiallyovercome the lack of accuracy. However, in some examples, a secondaryparameter can be used to provide even more accuracy. For example, thepower correction can be based on an output during a “tissue sampling”phase. If the tissue has one property, then a first power correction canbe used. If the tissue has another property, then a second powercorrection can be used. Examples of properties that can be used todetermine a power correction include, but are not limited to, the energydelivered over a period of time, calculated impedance, current draw,voltage phase angle, tissue temperature, and the like. The processor canuse these properties alone or in combination to select a powercorrection. For example, the processor can use both a tissue temperatureand a calculated impedance to select a power correction.

In examples that utilize one or more secondary parameters to determine apower correction, the measurement circuit can measure a representationof an impedance of the tissue positioned between two electrodes of theelectrosurgical device, compare the measured representation of impedanceto a first threshold, and if the impedance is less than a firstthreshold, e.g., 50 ohms, as described above with respect to FIG. 17,select a first power correction from two or more power corrections.Then, the control circuit can compare a representation of one or moresecondary parameters to one or more thresholds.

When the representation of one (or more) secondary parameters is lessthan one (or more) thresholds, the control circuit can select betweenthe previously selected first power correction and one or more otherpower corrections. The control circuit can determine that the previouslyselected first power correction is adequate or it can determine, basedon the secondary parameter, e.g., output current of the power generator,a tissue temperature, and a voltage phase angle, that a different powercorrection would be desirable to apply to a power setting.

In some examples, if the impedance is less than a first threshold, e.g.,50 ohms, the control circuit can select the secondary power correction.As the impedance increases, the control circuit can then select thefirst power correction. As the increases continues to increase, thetuned power setting can utilize the standard generator control withoutany power correction.

In some examples, the power corrections can be used for specific periodsof time, e.g., using tissue feedback. For example, using the correctedpower setting, the control circuit can deliver electrosurgical energyvia the electrodes of the electrosurgical device during a period of timeover a range of impedance values or until an amount of energy isapplied, or a combination of both. In addition, external metrics can beapplied such as time periods or user settings.

FIG. 24 is a flow diagram depicting another example of power correctiontechniques that can be used in a surgical system. FIG. 24 depicts atwo-decision flow diagram that can use impedance to decide which powercorrection to apply. In addition, the flow diagram can also useimpedance as a decision point for when to apply the power correction andwhen to stop applying the power correction.

At block 2400, stage 1A can be complete and the generator output canstabilize. At block 2402, stage 1B can begin and the control circuit candetermine an average impedance of tissue during the last 50 ms of stage1B. At block 2404, the control circuit can determine whether the averageimpedance is between 0-20 ohms. If the average impedance is between 0-20ohms (“YES” branch of block 2404), then at block 2406 the controlcircuit can use a first power correction value “X” for stage 2.

If the average impedance is not between 0-20 ohms (“NO” branch of block2404), then at block 2408 the control circuit can determine whether theaverage impedance is between 20.01-50 ohms. If the average impedance isbetween 20.01-50 ohms (“YES” branch of block 2408), then at block 2410the control circuit can use a second power correction value “Y” forstage 2. If the average impedance is not between 20.01-50 ohms (“NO”branch of block 2408), then at block 2412 the control circuit candetermine that no power correction is needed for stage 2.

Reduced Thermal Margin Combination Energy Device (FIGS. 18 and 19)

Surgical systems exist that can deliver two types of energy: ultrasonicenergy and electrosurgical energy, such as high-frequency energy. Theultrasonic energy can provide rapid and precise cutting of tissue andthe electrosurgical energy can provide reliable vessel sealing. Thesystem can deliver the two types of energy simultaneously or the systemcan control the delivery such that the two types of energy are deliveredseparately.

FIG. 18 is a simplified block diagram of an example of a combinationultrasonic energy and electrosurgical energy system that can implementvarious techniques of this disclosure. The system 1400 can include asurgical device 1402 coupled to an ultrasonic drive unit 1404 and anelectrosurgical drive unit 1406. Additional information regarding suchcombination ultrasonic energy and electrosurgical energy systems can befound in commonly assigned U.S. Pat. No. 8,574,228 to Okada et al. andtitled “ULTRASOUND TREATMENT SYSTEM”, the entire contents of which beingincorporated herein by reference. The surgical device 1400 can includeultrasonic transducer 1408 and a probe 1410. The ultrasonic drive unit1404 can include a first output circuit 1412 configured to generate adriving signal that is applied to the ultrasonic transducers 1408 togenerate ultrasonic vibrations that are conveyed to biological tissuevia probe 1402.

The system 1400 can include a control circuit configured to controlvarious aspects of the operation of the ultrasonic drive unit 1404 andthe electrosurgical drive unit 1406. For example, the control circuit1414 can be configured to generate and apply signals to the first outputcircuit 1412 of the ultrasonic drive unit 1404 and configured togenerate and apply signals to a second output circuit 1416 of theelectrosurgical drive unit 1406. In some example configurations, thecontrol circuit 1414 can include components similar to and operatesimilar to the control circuit 48 of FIG. 2. In some exampleconfigurations, the electrosurgical drive unit 1406 can includecomponents similar to and operate similar to the electrosurgicalgenerator 12 of FIG. 2. The second output circuit 1416 can generate highfrequency electrotherapeutic signals to be delivered to biologicaltissue via the probe 1410. The first and second output circuits 1412,1416 are coupled to the control circuit 1414 and configured to generateand deliver energy to an output terminal of the system for delivery to apatient. In some examples, the system can include a speaker 1418 and/ordisplay 1422 to provide an alarm or other audible notification and/or avisual notification to a user.

In some examples, the surgical device 1402 can be similar to thesurgical device FIG. 1 of commonly assigned U.S. Patent ApplicationPublication No. US 20120010539 to Yachi et al. and titled OPERATIONDEVICE AND SURGICAL APPARATUS,” the entire contents of which beingincorporated herein by reference. The surgical device of FIG. 1 of U.S.Patent Application Publication No. US 20120010539 can perform atreatment such as incision, resection, and the like of the living tissueby utilizing the ultrasonic waves together with the application of thehigh-frequency waves. In addition, it is also possible to perform acoagulation treatment of the living tissue by utilizing the ultrasonicwaves.

In some examples, the electrosurgical drive unit 1406 can include ameasurement circuit 1420. The measurement circuit 1420 can be similar tothe measurement circuit 46 of FIG. 2 and can be configured to measureone or more electrical parameters of biological tissue coupled to thesurgical device 1402.

Appropriate power delivery can be an important factor to gaining optimaltissue performance in vessel sealing. Too much energy too quickly cancause steam pockets to form within the tissue, which can cause damage totissue surrounding the surgical device. This phenomenon is often termed“thermal margin”. Combination ultrasonic energy and electrosurgicalenergy systems often use waveforms such as a constant pulse rate orramped output of high frequency energy, e.g., RF energy, along withultrasonic energy and layer them on top of each other. This can resultin undesirable consequences, such as surgical device tips getting hotand thermal margins increasing.

The present inventors have recognized the need in a combinationultrasonic energy and electrosurgical energy system to monitor feedbackfrom the tissue to determine whether a desirable steam pocket has beencreated. Using various techniques described below, the combinationultrasonic energy and electrosurgical energy system can monitor feedbackfrom the tissue, such as a change in the current drawn, a change in theimpedance value, or a change in the impedance over time, to provide anindication that a desirable steam pocket has been created. At thispoint, instead of continuing to apply energy to the tissue, one or bothof the high frequency energy, e.g., RF energy, and the ultrasonic energycan be reduced or stopped.

A non-limiting specific example of using a combination ultrasonic energyand electrosurgical energy system, e.g., the system 1400 of FIG. 18, tomodify biological tissue using various techniques of this disclosurewill now be described. The combination ultrasonic energy andelectrosurgical energy system can deliver at least two modes of energy:a first mode including ultrasonic energy and second mode includingbipolar energy. A control circuit, e.g., the control circuit 1414 ofFIG. 18, can monitor feedback from the tissue in contact with thesurgical device by controlling a measurement circuit, e.g., themeasurement circuit 1420 of FIG. 18, to measure a representation of animpedance of the tissue. For example, the control circuit can monitor achange in the impedance value, which can indicate that a maximumpreferable amount of steam has been created in the tissue and furthersteam creation could lead to excessive thermal margin. In other exampleimplementations, the control circuit can monitor a change in the currentdrawn, and/or an impedance value, e.g., an absolute impedance value.

Once the change in impedance values meets or exceeds a threshold value,the control circuit can control the ultrasonic drive unit, e.g., theultrasonic drive unit 1404 of FIG. 18, to stop the ultrasonic output. Inaddition, the control circuit can control the electrosurgical driveunit, e.g., the electrosurgical drive unit 1406 of FIG. 18, to reducethe output of the high frequency electrotherapeutic signals generated bythe second output circuit 1416 of the electrosurgical drive unit 1406.For example, the high frequency output can be reduced to such an extentthat the generated steam in the tissue can partially or totally revertback to liquid. Once this liquid state is achieved, as determined by thecontrol circuit using a set time, feedback control, or both, the system1400 can apply power again, until such time, either the steam productionlimit is met, or the end of an energy application cycle is met, e.g.,either by user decision or by feedback control.

FIG. 19 is a flow diagram depicting an example of a reduced thermalmargin technique that can be used in a combination ultrasonic energy andelectrosurgical energy system. At block 1500, a control circuit cancontrol the delivery of energy to biological tissue positioned betweentwo electrodes of the electrosurgical device, where the delivered energyincludes at least some ultrasonic energy. For example, the controlcircuit 1414 of FIG. 18 can control the first output circuit 1412 todeliver ultrasonic energy and the second output circuit 1416 to deliverhigh frequency energy, e.g., RF energy, to tissue in contact with thesurgical device 1402 of FIG. 18. As an example, the surgical device caninclude an ultrasonic forceps with HF electrodes on its jaws.

At block 1502, a measurement circuit can measure a representation of atissue parameter, such as an impedance, of the biological tissue. Forexample, the measurement circuit 1420 of FIG. 18 to measure a change inthe current drawn, and/or an impedance value, such as an absoluteimpedance value or a change in impedance (a relative value).

At block 1504, the control circuit can reduce a level of or terminatethe delivery of energy based on a characteristic of the measuredrepresentation of the tissue parameter, of the biological tissue.Example characteristics can include but are not limited to thefollowing: resistance, impedance, current, phase angle, consumedcurrent, and/or required voltage, as well as changes (deltas) in one ormore of these characteristics, and combinations of thesecharacteristics. For example, the control circuit 1420 of FIG. 18 cancontrol the first output circuit 1412 of FIG. 18 to reduce the level ofultrasonic energy. In some examples, the control circuit 1420 cancontrol the first output circuit 1412 to terminate, or reduce, thedelivery of ultrasonic energy. Termination is an example of a reductionof the delivery of ultrasonic energy.

In some examples, the delivered energy can be modified, such as byincreasing the energy or by temporarily reducing it but allowing it toreturn to its previous level after a short interval. Temporarilyreducing the energy can mean temporarily reduce to, or near to, noenergy delivery, e.g., suspend.

In some examples, the control circuit can pause the delivery of energyto allow for steam condensing, in contrast to a pause in the energy asan endpoint to the activation. By pausing the delivery of energy, thesystem can establish a fluid condensation dwell time. The system doesnot need to monitor the tissue parameters to identify the endpoint of ajoint high frequency/ultrasound therapy pulse.

In other examples, the control circuit 1420 can control the first outputcircuit 1412 to reduce the level of electrosurgical energy. In someexamples, the control circuit 1420 can control the first output circuit1412 to terminate the delivery of electrosurgical energy.

The electrosurgical energy can be power-controlled orvoltage-controlled, for example, as described above. In apower-controlled implementation, the control circuit 1420 can controlthe second output circuit 1416 to deliver, e.g., according to a plan,regimen, or schedule, the electrosurgical energy using a product of thevoltage applied across the engaged biological tissue and the electricalcurrent output by second output circuit 1416. For example, the controlcircuit can control the second output circuit 1416 to deliver a constantpower or a monotonically increasing power during a particular phase,e.g., drying phase.

In a voltage-controlled implementation, the control circuit can controlthe voltage of the electrosurgical energy delivered by the second outputcircuit 1416, e.g., according to a plan, regimen, or schedule. Forexample, the control circuit can control the second output circuit 1416to deliver a constant voltage or a monotonically increasing voltageduring a particular phase, e.g., drying phase.

As mentioned above, the control circuit can reduce a level of orterminating the delivery of energy based on a characteristic of themeasured representation of impedance of the biological tissue. In someexamples, the characteristic of the measured representation of impedanceis an impedance value, such as an absolute value of impedance or arelative value. In some such examples, the control circuit can beconfigured to compare the measured impedance value to a threshold valueand reduce the level of or terminate the delivery of energy based on thecomparison. For example, the control circuit can reduce the level of,periodically reduce the level of, or terminate the delivery of one orboth of the ultrasonic energy and electrosurgical energy based on thecomparison. By periodically reducing the level, the system can reducethe power at various stages during a single output, where an output isduring the course of a full activation.

In other examples, the characteristic of the measured representation ofimpedance is a change in impedance value. In some such examples, thecontrol circuit can be configured to compare the change in impedancevalue to a threshold value and reduce the level of or terminate thedelivery of energy based on the comparison. For example, the controlcircuit can reduce the level of or terminate the delivery of one or bothof the ultrasonic energy and electrosurgical energy based on thecomparison.

Using the techniques described above for a combination ultrasonic energyand electrosurgical energy system, the overall power output of thesystem can be reduced when steam pockets are created, which can reduceundesirable thermal margins.

Staged Impedance Values to Control Thermal Margins in Systems with SlowCPUs (FIGS. 20 and 21)

There is often a desire to obtain high performance without increasingthe processing burden on a system. Slower systems, which may be lessexpensive to purchase or maintain, can perform better if processing iskept low.

Typically, steam control and thermal margin control of devices used forvessel sealing can be achieved by monitoring one or more feedbacksystems. This can be a single true feedback element or multiple feedbackelements that are interdependent, such as a calculation based on one ora number of events, or through a decision tree type structure.

An example of such a system can monitor a difference (or delta) betweenthe lowest encountered calculated impedance and a rolling upperimpedance. In other examples, a rate of impedance rise with respect totime, a change in phase angle, a change in current draw, and a change involtage can be used as indicators of steam generation within tissues.

In monitoring a difference (or delta) between the lowest encounteredcalculated impedance and a rolling upper impedance, for example, newer,fast reaction hardware can use a specific boundary or decision point todetermine whether an expected steam pocket has been created and, if so,whether the pocket is sized such that power should be reduced,momentarily stopped, or stopped completely. In older, slower reactionsystems, the speed at which the steam pocket is created is the same, butthe reaction time to reduce or stop the power is slower, which canresult in “steam pocket overshoots” that can cause greater thermalmargin.

By way of example, if an impedance threshold is set at 55 ohms, theolder, slower-to-react system can overshoot the 55-ohm threshold andstop at 70 ohms. In contrast, newer electrosurgical systems can includefaster analog-to-digital converters, processors, and other hardware thatcan allow sampling at millions of samples per second. In such systems,if an impedance threshold is set at 55 ohms, the newer system can stopat about the desired 55 ohms.

The present inventors have recognized the need to improve the thermalmargin control in legacy electrosurgical systems. Through extensiveobservation of tissue effects, the present inventors have recognizedthat overshoot typically occurs through the early pulse phases of anelectrosurgical waveform and that the rate of steam generation reducesthroughout the waveform as the tissue becomes desiccated through theexpulsion of fluid. Therefore, to solve the problem of overshoot andimprove the thermal margin control, the present inventors haverecognized the desirability of incorporating an intelligence within theoutput. In particular, the present inventors have recognized that theelectrosurgical system can count the pulses of the electrosurgicalsignal and can assign different values of the trigger or threshold,e.g., an impedance value or impedance delta, based on the pulse number.In this manner, the threshold value of one or more of the initialelectrosurgical energy pulses can be lowered, which can allow forovershoot and thus reduce the thermal margin of legacy electrosurgicalsystems.

FIG. 2, described above, depicts an example of a surgical system thatcan be used to implement various aspects of the thermal margin controltechniques of this disclosure. As shown in FIG. 1, the surgical systemof FIG. 1 can include an electrosurgical device such as the forceps 14.The forceps 14 can include two jaws, e.g., the first jaw member 36 andthe second jaw member 38. In some examples, one of the two jaws can bemoveable and the other jaw can be stationary. In other examples, bothjaws can be moveable.

It should be noted that the thermal margin control techniques of thisdisclosure are not limited to electrosurgical devices that include jaws.Rather, the thermal margin control techniques can be implemented usingdevices such as spatulas and snares.

The electrosurgical device, e.g., the forceps 14, can include two ormore electrodes sized, shaped, and/or otherwise configured to deliverthe electrotherapeutic signal to the biological tissue, e.g., the tissue16 of FIG. 1. In some examples, the electrodes can be integral with thejaws, e.g., the first jaw member 36 and the second jaw member 38, as inFIG. 1. In other examples, the electrodes can be coupled to the jaws.

An output circuit, such as including the power source 44 of FIG. 2, canbe configured to generate and deliver electrosurgical energy to anoutput terminal, e.g., the instrument interface 42 of FIG. 2, fordelivery to a patient. The output terminal can be configured to coupleto an electrosurgical device, such as the forceps 14 of FIG. 1, anddeliver electrosurgical energy, e.g., high frequency, such as RF energy,to biological tissue via electrotherapeutic signals. A control circuitof the surgical system, e.g., the control circuit 48 of the surgicalsystem of FIG. 1, can be coupled to the output circuit and the controlcircuit can be configured to perform various aspects of the thermalmargin control techniques.

FIG. 20 is a flow diagram depicting an example of a thermal margincontrol technique that can be used in an electrosurgical system. Atblock 1600, a user, such as a surgeon or clinician, can initiatedelivery of electrosurgical energy to the biological tissue of apatient, such as tissue positioned between two jaws of theelectrosurgical device. At block 1602, a control circuit, e.g., thecontrol circuit 48 of the system 10 of FIG. 2, can count the number ofthe delivered electrosurgical pulse.

At block 1604, the control circuit can compare a parameter to athreshold value. In some examples, the parameter can be an impedance ofthe biological tissue, a change in impedance (or delta) of thebiological tissue, a rate of change of the impedance of the biologicaltissue, a change in a current of the delivered electrosurgical energypulse, a change in an output voltage of the delivered electrosurgicalenergy pulse, or a change in a phase angle, e.g., the phase anglebetween the voltage difference delivered across and electrical currentconducted by the biological tissue. In some examples, a measurementcircuit, e.g., the measurement circuit 46 of FIG. 2, to measure theparameter or measure electrical characteristics that can be used by thecontrol unit, e.g., the processor 54 of FIG. 2, to calculate theparameter. In some examples, the control circuit can reduce the deliveryof the plurality of electrosurgical energy pulses when a measuredrepresentation of impedance meets or exceeds an endpoint value, e.g., anendpoint value of about 100-600 ohms.

At block 1606, the control circuit can adjust the threshold value basedon the count of the electrosurgical energy pulse. That is, the thresholdvalue can be changed from one pulse to another pulse. For example, for asecond pulse, the control circuit can adjust the impedance delta to 45ohms, e.g., up from 40 ohms. In this manner, the control circuit can seta threshold value or boundary based on the count of the pulse. Tailoringthe threshold value of one or more of the initial electrosurgical pulsesbased on the count of the pulse can help account for any overshootcaused by the delay in older, slower-to-react electrosurgical generatorsystems.

By way of a non-limiting example, it can be desirable to deliver anenergy pulse that creates a change in impedance (or an impedance delta)of about 55 ohms in biological tissue. When a user initiates delivery ofa first pulse of electrosurgical energy, the control circuit, e.g., thecontrol circuit 48 of FIG. 2, can reset a counter, e.g., within theprocessor 54 of FIG. 2, and set a threshold value of a parameter, e.g.,a change in impedance, to a first value. For example, the controlcircuit can retrieve data representing the threshold value for a firstpulse from a memory device, e.g., the memory 56 of FIG. 2, and set thethreshold value of an impedance delta for a first pulse to the retrieveddata, e.g., representing 40 ohms.

The system can deliver the first pulse of energy and the control circuitcan compare a measured parameter, e.g., the impedance delta, to thethreshold value of 40 ohms. Once the measured parameter reaches 40 ohms,the control circuit can stop delivery of the first pulse. Because of thedelay in older, slower-to-react electrosurgical generator systems, thesystem can overshoot the 40-ohm threshold and can actually stop once theimpedance delta reaches about 55 ohms. The lowered threshold value forthe first pulse can allow for the rapid rise of the first pulse, withovershoot, providing an actual impedance of 55 ohms due to slow reactionof the system. As mentioned above, in some examples, an impedance delta55 ohms can be desirable.

Next, in preparation for delivering a second pulse, the control circuitcan adjust the threshold value based on the count of the electrosurgicalpulse. Here, the count is two and the control circuit can retrieve datarepresenting the threshold value for a second pulse from the memorydevice and set the threshold value of the impedance delta for a secondpulse to the retrieved data, e.g., representing 45 ohms.

The system can deliver the second pulse of energy and the controlcircuit can compare the measured parameter to the adjusted thresholdvalue of 45 ohms. Once the measured parameter reaches 45 ohms, thecontrol circuit can stop delivery of the second pulse. Because of thedelay, the system can overshoot the 45-ohm threshold and can actuallystop once the impedance delta reaches about 55 ohms. The adjustedthreshold value for the second pulse can allow for the slightly slowerramp rate of the second pulse, providing an actual impedance of 55 ohmsdue to slow reaction of the system.

Next, in preparation for delivering a third pulse, the control circuitcan adjust the threshold value based on the count of the electrosurgicalpulse. Here, the count is three and the control circuit can retrievedata (or use previously retrieved data) representing the threshold valuefor a third pulse from the memory device and set the threshold value ofthe impedance delta for a third pulse to the retrieved data, e.g.,representing 55 ohms.

The system can deliver the third pulse of energy and the control circuitcan compare the measured parameter to the adjusted threshold value of 55ohms. Once the measured parameter reaches 55 ohms, the control circuitcan stop delivery of the third pulse. With the third pulse, the ramprate can be slow enough that the system can react in time and stop oncethe impedance delta reaches 55 ohms.

In this manner, the threshold value of one or more of the initialelectrosurgical energy pulses can be artificially lowered in that thedesired threshold of 55 ohms, for example, remains the same despite theadjustments of 40 ohms, 45 ohms, etc. This artificial lowering of thethreshold can allow for overshoot and thus reduce the thermal margin oflegacy electrosurgical systems. Threshold values for additional pulses,such as the fourth, fifth, and higher pulses, may not need to beadjusted. For example, the fourth, fifth, and higher pulses can be setat 55 ohms, for example. In other examples, the third, fourth, fifth,and higher pulses can be adjusted.

In addition to the stratified pulse capability described above, thecontrol circuit can use predictors to determine or select a set of pulseratios to use. For example, a ratio can be between each of the adjustedthreshold values to the desired threshold value. By way of non-limitingexamples for purposes of illustration only, if the desired threshold is55 ohms and the first, second, and third pulse thresholds are 40, 45,50, respectively, the ratios can be 40/55, 45/50, and 50/55.

The predictors can identify the likelihood of impedance rise and allowfor that in the calculation of the adjusted threshold values. Forexample, a tissue with a high initial impedance that drops to a lowimpedance in the first pulse can indicate a rapid rise and therefore apercentage reduction in the impedance delta being searched for. This canbe because tissue with a higher initial impedance that drops suddenlycan be indicative of tissue with a lot of fluid and therefore rapidsteam rise. However, a tissue for which the impedance delta starts lowand goes lower can have a different ratio selector or set of thresholdvalues.

Various parameters that can be used as predictors can include animpedance of the biological tissue, a change in impedance (or delta) ofthe biological tissue, a rate of change of the impedance of thebiological tissue, a change in a current of the deliveredelectrosurgical energy pulse, a change in an output voltage of thedelivered electrosurgical energy pulse, or a change in a phase angle,e.g., the phase angle between the voltage difference delivered acrossand electrical current conducted by the biological tissue.

In some examples, the control circuit, e.g., the control circuit 48 ofFIG. 2, can compare a first measured parameter to a second measuredparameter and adjust the threshold value based on a difference betweenthe first measured parameter and the second measured parameter. Forexample, a measurement circuit, e.g., the measurement circuit 46 of FIG.2, can measure a first impedance delta, e.g., before a first pulse isdelivered, and a second impedance delta, e.g., after the first pulse isdelivered. Based on the difference between the first and secondimpedance deltas, the control circuit can select a particular set ofadjusted impedance.

As a non-limiting example, the control circuit can have initiallyselected a first set of adjusted impedance delta threshold values forthe first, second, and third pulses, such as 40 ohms, 45 ohms, and 55ohms, respectively. However, based on the difference between the firstand second impedance deltas, the control circuit can select a second setof adjusted impedance delta threshold values for the first, second, andthird pulses, such as 45 ohms, 50 ohms, and 55 ohms, respectively.

In some examples, the control circuit can adjust the threshold valuebased on the first measured parameter being greater than the secondmeasured parameter. In other examples, the control circuit can adjustthe threshold value based on the first measured parameter less than thesecond measured parameter. In some examples, the control circuit canadjust the threshold value based on the rate of change between the firstmeasured parameter and a second measured parameter.

Other factors can also be used to predict the correct ratios to use. Forexample, the rate of decrease with respect to time of the initialimpedance can be used to indicate the rate of rise and therefore thecorrect threshold value or trigger. In addition, the initial impedanceor even the prior tissue activation can be used to as predictors. Priorissue activation can be the last time that the surgeon, for example,grasped tissue and pushed the activation button.

FIG. 21 is a flow diagram depicting another example of a thermal margincontrol technique that can be used in an electrosurgical system. Acontrol circuit, e.g., the control circuit 48 of the system 10 of FIG.2, can count the number of the delivered electrosurgical pulse. In someexamples, the control circuit can retrieve data representing the first(and more) threshold values from a memory device, such as the memory 56of FIG. 2. At block 1700, a user, such as a surgeon or clinician, caninitiate delivery of a first electrosurgical energy pulse to thebiological tissue of a patient, such as tissue positioned between twojaws of the electrosurgical device.

At block 1702, the control circuit can compare a first measuredrepresentation of impedance, e.g., an impedance delta, of the biologicaltissue to a first threshold value, e.g., 40 ohms. In some examples, themeasured representation of impedance can be an impedance of thebiological tissue, a change in impedance (or delta) of the biologicaltissue, a rate of change of the impedance of the biological tissue, or achange in a current of the delivered electrosurgical energy pulse. Insome examples, a measurement circuit, e.g., the measurement circuit 46of FIG. 2, to measure the representation of impedance or measureelectrical characteristics that can be used by the control unit, e.g.,the processor 54 of FIG. 2, to calculate the representation ofimpedance. In some examples, the control circuit can reduce the deliveryof the plurality of electrosurgical energy pulses when a measuredrepresentation of impedance meets or exceeds an endpoint value, e.g., anendpoint value of about 250-350 ohms.

At block 1704, the control circuit can reduce or terminate delivery ofthe first electrosurgical energy pulse when the first measuredrepresentation of impedance meets or exceeds the first threshold value.For example, the control circuit can reduce or terminate delivery of thefirst pulse when the measured impedance delta meets or exceeds the40-ohm threshold value associated with the first pulse.

At block 1706, the control circuit can increase the first thresholdvalue to a second threshold value based on the count of the pulse. Forexample, based on the count being two, the control circuit can increasea 40-ohm impedance delta threshold value associated with the first pulseto a 45-ohm threshold impedance delta value associated with the secondpulse.

At block 1708, the control circuit can control the electrosurgicalgenerator, e.g., electrosurgical generator 12 of FIG. 2, to deliver asecond electrosurgical energy pulse to the tissue. At block 1710, thecontrol circuit can compare a second measured representation ofimpedance, e.g., an impedance delta, of the biological tissue to thesecond threshold value, e.g., 45 ohms. At block 1712, the controlcircuit can reduce or terminate delivery of the second electrosurgicalenergy pulse when the second measured representation of impedance meetsor exceeds the second threshold value. For example, the control circuitcan reduce or terminate delivery of the second pulse when the measuredimpedance delta meets or exceeds the adjusted 45-ohm threshold value ofthe second pulse.

In some examples, in preparation for delivering a third pulse, thecontrol circuit can adjust the threshold value based on the count of theelectrosurgical pulse. Here, the count is three and the control circuitcan retrieve data (or use previously retrieved data) representing thethreshold value for a third pulse from the memory device and set thethreshold value of the impedance delta for a third pulse to theretrieved data, e.g., representing 55 ohms.

As described above with respect to FIG. 20, predictors can be used todetermine or select a set of pulse ratios to use. For example, thecontrol circuit, e.g., the control circuit 48 of FIG. 2, can compare afirst measured parameter to a second measured parameter and adjust thethreshold value based on a difference between the first measuredparameter and the second measured parameter. For example, a measurementcircuit, e.g., the measurement circuit 46 of FIG. 2, can measure a firstimpedance delta, e.g., before a first pulse is delivered, and a secondimpedance delta, e.g., after the first pulse is delivered. Based on thedifference between the first and second impedance deltas, the controlcircuit can select a particular set of adjusted impedance.

By using the thermal margin control techniques described above, e.g.,with respect to FIGS. 20 and 21, the threshold value of one or more ofthe initial electrosurgical energy pulses can be artificially lowered.This artificial lowering of the threshold can allow for overshoot andthus reduce the thermal margin of legacy electrosurgical systems.

Although described separately, the two-boundary threshold techniques,open circuit check techniques, power correction techniques, reducedthermal margin techniques for combination ultrasonic energy andelectrosurgical energy systems, and thermal margin control techniquesdescribed above can be implemented individually or in combinations oftwo or more of the techniques described in this disclosure, as desired.

For example, a system that implements the two-boundary thresholdtechniques can also implement one or more of the power correctiontechniques, reduced thermal margin techniques for combination ultrasonicenergy and electrosurgical energy systems, and thermal margin controltechniques described above. By way of a non-limiting example, forpurposes of illustration only, a system that implements the two-boundarythreshold techniques can also implement the thermal margin controltechniques that can artificially lower threshold values.

In another non-limiting example, for purposes of illustration only, acombination ultrasonic energy and electrosurgical energy systems thatimplements reduced thermal margin techniques by reducing a level of orterminating the delivery of energy based on a characteristic of ameasured representation of impedance of the biological tissue can alsoimplement power correction techniques that can apply a power correctionto the power control of the electrosurgical generator based on whether ameasured impedance is within a range of impedances, e.g., 0-20 ohms.

Consumed Energy Monitoring and Open Circuit Evaluation (FIGS. 22A-22D)

To assist with determining whether to continue with additional tissuedrying phases, the present inventor has recognized that at the end of adrying phase, the amount of energy (and/or charge) delivered to thetissue during the just completed drying phase (or just completedinterrogation phase and drying phase) can be evaluated, as described indetail below. If the amount of energy (and/or charge) applied is belowthe energy (and/or charge) threshold value and has created a sufficientimpedance delta value, then the tissue is sufficiently dry, and theprocess can continue to the next stage. However, if the amount of energy(and/or charge) applied is above the energy (and/or charge) thresholdvalue and has created a sufficient impedance delta value, then thetissue is too wet and needs another drying phase.

FIGS. 22A-22D depict a flow diagram of an example of an energy deliverytechnique that can use, among other things, an amount of energydelivered to a biological tissue in its decision-making process.Although the technique depicted in the flow diagram of FIGS. 22A-22D isdescribed as power-controlled, in some examples, the technique can bevoltage-controlled.

Three steps are depicted in the flow diagram of FIGS. 22A-22D and aredescribed in detail below. The portion of the flow diagram labeled Step1, which can be an interrogation phase or other low energy phase, can bea power-controlled step (or, in other examples, a voltage-controlledstep) where an electrosurgical generator, such as the electrosurgicalgenerator 12 of FIG. 2, can control delivery of a low powerelectrotherapeutic signal, such as 10 W, to the biological tissue. Insome examples, Step 1 can considered to be a steam-dissipation phase inwhich steam in the tissue generated during Step 2 is allowed todissipate in order to prevent thermal margins.

In some examples, Step 1 can be set to run for a specific duration, suchas 250 ms, during which time the electrosurgical generator can controlthe power as closely as possible to ensure a consistent delivery level.During Step 1, a control circuit, such the control circuit 48 of FIG. 2,in combination with a measurement circuit, such as the measurementcircuit 46 of FIG. 2, can track various parameters. For example, thecontrol circuit and the measurement circuit can begin measuring andstoring the maximum and minimum impedances associated with a particulardelivered pulse (pulse RMax and pulse RMin)(also tracked in Step 2). Inaddition, during the application of power in Steps 1 and 2, the controlcircuit and the measurement circuit can store the values of the amountof energy (and/or charge) delivered to the tissue.

The amount of energy delivered to the tissue can be measured in joulesand is the integration of the amount of power delivered in watts. Theamount of charge delivered to the tissue can be measured in coulombs andis the integration of amount of current in amps. Although generallyshown and described below with respect to an amount of energy deliveredto the tissue, the techniques of FIGS. 22A-22D can additionally oralternatively use an amount of charge delivered to the tissue.

The method shown in FIG. 22A begins at block 1800 with the power of theelectrosurgical generator, such as the electrosurgical generator 12 ofFIG. 2, turned ON. At block 1802, the method enters Step 1 and theelectrosurgical generator can deliver a constant power output “A” for aduration of time “B”. At block 1804, the measurement circuit and thecontrol circuit can read or calculate the impedance values of the tissueand then the control circuit can average those values. In some examples,the average impedance determined during Step 1 can have an effect on theramp rate selected for applying energy in Step 2, the next power-controlphase.

In FIG. 22B at block 1806, the method enters Step 2, which can be adrying phase. At block 1806, the control circuit can automaticallyselect a power ramp rate based on the impedance value determined in Step1. Different bands or ranges of impedance values can result in differentoutput power ramp rates. For instance, for a lower impedance range, suchas 1 ohm to 15 ohms, the control circuit can select a ramp rate “E”(block 1808)(such as 0.05 W/ms), while for a medium impedance range,such as 15 ohms to 75 ohms, the control circuit can select a ramp rate“D” (block 1810)(such as 0.035 W/ms),and for a high impedance range,such as 75 ohm to 400 ohms, the control circuit can select a power ramprate “F” (block 1812)(such as 0.035 W/ms). In some examples, there canbe only two ramp rates, such as a fast first ramp rate and a slowersecond ramp rate, such as shown in FIG. 4 in t1-t2 and t2-t3. At block1814, after the power ramp rate has been selected, the control circuitcan set the cumulative pulse energy (and/or charge) value to 0 and applypower to the tissue via an electrotherapeutic signal at block 1816.

Next, the method can perform activities in parallel, including thecontrol circuit reading or calculating the impedance of the tissue atblock 1818 and reading or calculating the energy (and/or charge) appliedduring this particular pass at block 1820. In some examples, rather thanbeing run in parallel, the activities can be mixed in a single process.

At block 1820, the control circuit can read and calculate the energy(e.g., in joules) (and/or charge, e.g., in coulombs) applied during thispass to the biological tissue. Then, at block 1822, the control circuitcan add the energy (and/or charge) applied during this pass to the pulseenergy (and/or charge) value to generate a cumulative applied energy(and/or charge) value.

In the example shown in FIG. 22A and in parallel with the calculation ofthe energy applied, after calculating the impedance in block 1818, thecontrol circuit 48 of FIG. 2 can determine at block 1824 whether theimpedance is lower than a previous impedance Rmin. In some examples, indetermining the minimum impedance Rmin, the control circuit can startwith a default initial impedance, such as 1000 ohms. If the nextmeasured or calculated impedance is 20 ohms, for examples, then 20 ohmsis the new minimum impedance Rmin. Similarly, if a subsequent measuredor calculated impedance is 15 ohms, then 15 ohms is the new minimumimpedance Rmin. The minimum impedance Rmin can be from Step 1 or from apresent impedance reading.

If the present impedance reading is lower than a previous impedance Rmin(“YES” branch of block 1824), then at block 1826 the control circuit canstore the present impedance reading as the new minimum resistance valueRmin. Then, at block 1828, the control circuit can increase the power,such as along a specific power ramp rate trajectory (power increasedagainst time).

At block 1830, the control circuit can determine whether the power isgreater than a maximum power level for Step 2 (power “H”). If the poweris not greater than the maximum power level (“NO” branch of block 1830),then the process returns to block 1816 and another pass is started.However, if the power is greater than the maximum power level (“YES”branch of block 1830), then the control circuit can adjust or change thepower ramp rate to a second ramp rate at block 1832. In some examples,the second ramp rate is slower than the first ramp rate.

At block 1834, the control circuit can determine whether the appliedpower is greater than the maximum power level. If the power is notgreater than the maximum power level (“NO” branch of block 1834), thenthe process returns to block 1816 and another pass is started. However,if the power is greater than the maximum power level (“YES” branch ofblock 1834), then the control circuit can change the power ramp rate tothe maximum power level setting at block 1836 and then the processreturns to block 1816 and another pass is started.

Referring back to decision block 1824, if the present impedance readingis not lower than a minimum impedance Rmin (“NO” branch of block 1824),then the control circuit can determine whether the present impedancereading is greater than the minimum impedance Rmin plus an impedancedelta at block 1838. If the present impedance reading is not more thanthe minimum impedance Rmin plus the impedance delta (“NO” branch ofblock 1838), then the control circuit can move to block 1828 and themethod can continue as described above.

In some examples and in contrast to determining whether the measuredelectrical current is less than the predetermined faction of the maximumelectrical current at step 1824, the control circuit 48 can determinewhether the measured electrical current is less than the predeterminedfraction (or offset) of a current value measured at a predetermined timeinterval following the initiation of the pulse. For impedance monitoringsystems, the control circuit 48 can determine whether the measuredimpedance is greater than the predetermined fraction (or offset) of aresistance value measured at a predetermined time interval following theinitiation of the pulse.

However, if the present impedance reading is more than the minimumimpedance Rmin plus the impedance delta (“YES” branch of block 1838),then the control circuit can move to decision block 1840. By way of anon-limiting example, the impedance delta can be 55 ohms, the presentimpedance reading can be 75 ohms, and the minimum impedance Rmin can be15 ohms. In this non-limiting example, the present impedance reading,e.g., 75 ohms, is more than the minimum impedance Rmin, e.g., 15 ohms,plus the impedance delta, e.g., 55 ohms (“YES” branch of block 1838),then the control circuit can move to decision block 1840.

As described above, the control circuit determined whether there was aset difference between the present impedance reading and the minimumimpedance Rmin. If the difference was greater than a set amount, e.g.,55 ohms, then the control circuit can now check how much energy wasdelivered during the previous Step 1 and the current Step 2 phase atthis point in time. At block 1840, the control circuit can determinewhether the amount of energy (or charge) applied is less than an energythreshold value (or charge threshold value), such as 20 Joules (or 2Coulombs of charge). If the amount of energy applied is not less theenergy threshold value (“NO” branch of block 1840), then the controlcircuit can reset the minimum impedance Rmin and return to Step 1 atblock 1842. Eventually, the system will return to a second drying cyclein Step 2. In this manner, the control circuit can control the energydelivery of the therapeutic signal provided to the engaged biologicaltissue during a second drying phase if the amount of energy deliveredexceeds the threshold energy value.

However, if the amount of energy applied (or charge applied) is less theenergy threshold value (or charge threshold value) (“YES” branch ofblock 1840), then the control circuit can end the pulse and go to Step 3as shown at block 1844. In this manner, the control circuit can controlthe energy delivery of the therapeutic signal provided to the engagedbiological tissue during a finishing phase if the amount of energydelivered is less than the threshold energy value.

Step 3, which can be a finishing phase, begins at block 1846 in FIG.22C. At block 1846, the control circuit can store or record the targetfinal impedance. In some examples, the target final impedance can be aset final number. In some examples, the target final impedance can be adelta calculation from the lowest impedance value read or calculated inthis step plus a predetermined percentage or delta value. For example,if the minimum impedance Rmin for this step is measured to be 20 ohms,then a predetermined delta of 280 ohms can be added to the final targetimpedance, to set the value of the target final impedance to be 300ohms. In some examples, the target final impedance can be a deltacalculation from an impedance measurement taken after a predeterminedtime interval following the initiation of the pulse plus a predeterminedpercentage or delta value.

In some examples, the target final impedance can be dependent on thenumber of pulses, such as drying pulses. For example, if the end pointis dependent on the pulse number and if two pulses are delivered to thetissue, then the final impedance value might be 320 ohms. However, iffive pulses are delivered to the tissue, then the final impedance mightbe 280 ohms. If the endpoint is not achieved within a predeterminedamount of time, such as 2 seconds, then the method can return to Step 1in an attempt to further drive fluid from the tissue and reach asatisfactory end point impedance.

At block 1848, the control circuit can reset and initiate a timer, suchas in response to a delivery of electrosurgical energy to the biologicaltissue, such as positioned between two jaws of the electrosurgicaldevice or in contact with one or more electrodes. If a predeterminedimpedance delta between the present impedance reading and the minimumimpedance Rmin for this pulse is not met before a time interval isreached, then the output is returned to the first step, as this mayindicate that the tissue still contains too much water.

At block 1850, the control circuit can set the power output to powerlevel “I”. In some examples, the control circuit can control delivery ofthe electrotherapeutic signal to the tissue using a constant power ramprate. In some examples, the constant power ramp rate of Step 3 can beslower than the previous ramp rates, such as in Step 2. The controlcircuit can continue delivery using the constant power ramp rate until afinal impedance value is reached, such as 320 ohms in a non-limitingexample.

At block 1852, the control circuit can begin monitoring the impedance ofthe tissue. As described below, the control circuit can compare, e.g.,intermittently, a representation of impedance of the biological tissueto a threshold value, such as at blocks 1862 and 1872, and continue thedelivery of electrosurgical energy until the threshold value is met. Atblock 1854, the control circuit can increase the power to a constantpower ramp rate “J”. In some examples, before delivering theelectrosurgical energy at the constant power ramp rate, the controlcircuit can deliver the electrosurgical energy at a constant power.

At block 1856, the control circuit can determine whether the power isgreater than a maximum Step 3 power level. If the power is greater thanthe Step 3 maximum power level (“YES” branch of block 1856), then thecontrol circuit can set the power to the Step 3 maximum power level atblock 1858 in FIG. 22D. After either setting the power to the Step 3maximum power level at block 1858 or if the power is not greater thanthe Step 3 maximum power level (“NO” branch of block 1856), then thecontrol circuit can compare the timer value to the time interval “R” atdecision block 1860.

If the timer value is not greater than or equal to the time interval “R”(“NO” branch of block 1860), then the method can return to block 1854and the control circuit can increase the power. However, if the timervalue is greater than or equal to the time interval “R” (“YES” branch ofblock 1860), then the control circuit can determine if the impedance isgreater than the minimum value within this pulse plus a predetermineddelta impedance at block 1862, where the predetermined delta impedanceis the difference between the measured impedance and the lowest value ofthe impedance measured in the pulse.

If the control circuit determines that the impedance is not greater thanthe target impedance minus a predetermined delta impedance (“NO” branchof block 1862), then the method can return to Step 1 as shown at block1864. In this manner, the control circuit can reduce or terminate theenergy delivery during the therapeutic phase in response to themeasured, e.g., intermittently, impedance changing by a predetermineddelta impedance value.

However, if the control circuit determines that the impedance is greaterthan the target impedance minus a predetermined delta impedance (“YES”branch of block 1862), then the method can move to block 1866 andincrease the power to power ramp rate “J”.

At decision block 1868, the control circuit can determine whether thecurrent power is greater than the maximum Step 3 power level. If thecurrent power is greater than the maximum Step 3 power level (“YES”branch of block 1868), then the control circuit can reset the power tothe maximum step 3 power level “Q” at block 1870.

After either setting the power to the Step 3 maximum power level atblock 1870 or if the power is not greater than the Step 3 maximum powerlevel (“NO” branch of block 1868), then the control circuit candetermine whether the impedance is greater than the target finalimpedance “P” at block 1872. If the control circuit determines that theimpedance is greater than the target final impedance (“YES” branch ofblock 1872), then the seal is complete, and the control circuit can turnthe electrosurgical generator OFF at block 1874. However, if the controlcircuit determines that the impedance is not greater than the targetfinal impedance (“NO” branch of block 1872), then the control circuitcan determine whether the timer is greater than the maximum Step 3output timer at block 1876.

If the timer is greater than the maximum Step 3 output timer (“YES”branch of block 1876), then the method can return to Step 1 as shown atblock 1878. For example, if the timer times out, this can be anindication that the tissue was not sufficiently desiccated during theprevious steps. However, if the timer is not greater than the maximumStep 3 output timer (“NO” branch of block 1876), then the method canreturn to block 1866 to increase the power ramp rate.

In some examples, the timer at block 1860 can be used to detect apotential open circuit condition. For example, if the jaws of anelectrosurgical device, such as the forceps 14 of FIG. 1, were openedduring the sealing procedure, the electrosurgical generator couldmistakenly determine that the accompanying rise in impedance was theresult of the tissue drying.

Non-limiting values for the parameters A-S in FIGS. 22A-22 are shownbelow in Table 1:

TABLE 1 A 10 W B 250 ms D 0.035 W/ms E 0.05 W/ms F 0.035 W/ms H 60 W I15 W J 0.035 W/ms P 320 ohms Q 100 W R 100 ms S 20 ohms

In accordance with this disclosure, during Step 3, the timer at block1860 can be started. Upon reaching the target final impedance (orthreshold value), the control circuit can record an elapsed time. If thetarget final impedance (or threshold value) is reached in a very shortperiod of time, such as before the threshold time limit, then thecontrol circuit can determine that an open circuit has occurred ratherthan a completed seal and declare an error state. In other words, thecontrol circuit can declare an error state if the elapsed time is lessthan a time limit. The time limit may be 50 ms, 100 ms, or another timeperiod.

For example, the control circuit can determine a difference between theminimum measured impedances Rmin and the current or maximum measuredimpedance and compare the determined difference to a predetermined deltaimpedance value. In some examples, the control circuit can increase apower ramp rate of the electrosurgical energy in response to thecomparison. The control circuit can continue to increase the power ramprate, such as at block 1854, until either the determined differencemeets or exceeds the predetermined delta impedance value, such as atblock 1862, or a power limit is reached, such as at block 1858.

However, in some examples, if the determined difference is equal to orgreater than the predetermined delta impedance value and the timer isgreater than the threshold time limit, the control circuit can declarean error state and generate an error signal. In some examples, the opencircuit error signal can cause the control circuit to communicate anerror message to the user, such as using the user interface 50 of FIG.2, and to quickly terminate power to the electrosurgical device.

In some examples, the control circuit does not terminate power on a timemark. Instead, the power can continue until the final impedance isreached. At this point, the control circuit can evaluate the timeinterval to see if mitigating actions are needed. For example, a timeinterval or threshold set too long can produce false negatives, e.g., agood seal is formed, but the system has determined that an open circuitis present), especially on thin tissue that seals quickly. A timeinterval or threshold set too short can produce false positives, e.g., agood seal is not formed, but the system does not detect an error), whichcan occur when the user slowly opens the jaws, for example.

Dwell Time Between Pulses

It can be desirable to deliver electrotherapeutic signals using pulsedwaveforms. Through the pulsing of an electrosurgical signal, the tissuebetween the device jaws can be heated. Without pulsing, the tissue canheat and as it passes through different temperature ranges, typicallyincreasing as more and more energy is applied, the fluid within thetissue can reach a boiling point. The boiling point can be dependent onthe composition of the fluid that is being boiled and also on thepressure at which the jaws are clamping the tissue (changing thepressure alters the boiling point). This results in steam generation.

The steam created can increase the tissue impedance and, as a result,less heating current flows through the tissue and more voltage is driveninto the tissue. The steam grows into steam pockets and, because thesteam changes phase as it evaporates, the volume of the pocket is nowmuch greater. This new greater volume further increases the impedanceand, as such, more voltage is required to achieve the same power input.In the meantime, the steam is now transitioning from its previouslocation between the jaws and extending into the surrounding tissues.

The higher voltages required to power through these steam pocketsresults in increased adherence of the tissues to the energy applicationsurface, such as the jaws, while the steam being exuded into thesurrounding tissues away from the application site is a negative calledthermal margin. The thermal margin can damage structure that were notintended for tissue modification and can ultimately result inpost-operative tissue necrosis and perforation of vital organs or organstructures. To overcome the propagation of steam pockets intosurrounding tissues and higher required driving voltages, one controlmethod currently utilized is pulsing.

Pulsing is where there is a pause in the application of energy deliveredto the tissue of such a level that can modify the tissue. In someexamples, the energy delivery is stopped for a period of time. In otherexamples, the energy level can be reduced to a level where the energydoes not have a significant tissue effect. It can be desirable to applyat least some energy to the tissue rather than stop delivery completelyto allow continuous feedback or almost instantaneous feedback of thetissue state to the control circuit.

In some approaches, a fixed period of 250 ms can be used as a pauseperiod or “dwell time” which can ensure the tissue steam pockets havesignificantly condensed before energy is reapplied. A dwell time is atime interval following a first pulse and preceding a second pulse. Ifdwell times less than 250 ms are used, the steam pockets may not besufficiently depleted, and the subsequent application of energy canrapidly reinstate the steam pockets.

Although typically true for the first pulse with shorter than a 250 mspause, it is less clear for the subsequent pulses. For a second pulse, adwell time such as 200 ms can be appropriate, depending on what volumeof tissue and its related water content exists between the jaws.Subsequent pulses may need even less time (for example, a fifth pulsemay need 50 ms or less) to allow the re-condensing of the now muchreduced fluid content between the device jaws.

During these “dwell times”, the fluid can migrate back into the targetissue. During a dwell time, the generator can provide a low power signalto the tissue, which is low enough to not trigger a tissue effect. Smalldecreases in tissue thickness are typically noted as the outcome ofvessel sealing and the extruded tissue contains fluid. Fluid can also bedriven out by the steam having high pressure and pushing more mobileelements out of the area between the device application plates, such asextracellular fluid.

Unfortunately, not all tissues have the same fluid levels or tissuefluid mobility, and not even the same amount of tissue thickness orwidth is grasped between the device jaws for each seal. As such, a fixedstandard reduction in a pause period between pulses may not provide aneffective or accurate pause time controller.

In addition, there can be a product pressure to shorten the totalactivation as much as possible. The conservative choice of estimating along dwell time and applying it even for dwell periods that do notrequire such a long time can extend total activation unnecessarily. Theunnecessary extension of the total activation can lengthen surgery timesand can increase user fatigue, among other things.

To overcome the problems mentioned above, the present inventors haverecognized that the control circuit can utilize characteristics knownabout the tissue between the jaws to accurately predict the mostappropriate reduced pause period. For example, the control circuit canquery a stored data set, such as a look up table, and using one or moreknown characteristics about the tissue can determine a reduced pauseperiod or “dwell time”. The reduced dwell time can reduce the totalactivation time of the seal cycle, without impacting low thermal marginsand while still providing high confidence in a reliable seal.

In some examples, a control circuit, such as the control circuit 48 ofFIG. 2, can deliver first and second electrosurgical energy pulses tobiological tissue in electrical communication with, such as physicallyengaged to, positioned between, or otherwise coupled to, two electrodesof the surgical device, where the first and second electrosurgicalenergy pulses are separated from one another by a corresponding dwelltime. The control circuit can then determine the dwell timecorresponding to at least one of the electrosurgical energy pulsesfollowing the first electrosurgical energy pulse.

In some examples, a control circuit, such as the control circuit 48 ofFIG. 2, can determine and use the amount of energy applied to the tissueto determine an optimized dwell time. The amount of fluid between thedevice jaws requires a particular amount of energy in order to boil at aknown energy application rate. The control circuit can estimate how muchfluid is present by determining how much energy was delivered to thejaws to create a thermodynamic change to the tissue. The control circuitcan query the stored data set using the determined amount of energydelivered to identify an appropriate corresponding dwell time. For largesteam generation pulse cycles created using large amounts of energy, thecontrol circuit can provide a longer dwell time to condense, and forsmaller steam generation pulse cycles created using smaller amounts ofenergy, the control circuit can provide a shorter dwell time tocondense.

In other examples, rather than use a stored data set, such as a look uptable, the control circuit can determine a dwell time as a ratio of thedetermined energy applied to the jaws. In other examples, the controlcircuit can determine a dwell time as a factor of the determined energyapplied to the jaws. As a non-limiting example, if the energy applied tothe jaw was 20 joules, then the wait time can be 200 ms (X*10 ms). So,30 joules can correspond to 300 ms. The equation X*10 is an example andnot intended to be limiting. It can also be part of a logarithmic scaleor other math-based ratio term.

In addition, the period of time it takes to boil tissue between the jaws(at a set or known variable power) is another way of determining a dwelltime long enough to ensure that sufficient condensation mechanisms haveoccurred before applying the next tissue modifying level of energy tothe tissue. In some examples, the control circuit can attempt to cut thepower off short of boiling or with a little boiling as possible. Thecontrol circuit can determine that a longer dwell time is needed if ittakes a longer period of time to boil tissue as more energy would havebeen delivered to the tissue. For example, the control circuit caninitiate a timer upon delivering a pulse, determine whether the tissuehas boiled or is close to boiling and if so, stop the timer, compare thetimer to one or more values associated with corresponding dwell times,and determine or select a dwell time based on the comparison. As thetimer value increases, the dwell times can be increased. As non-limitingexamples for purposes of illustration only, a 250 ms dwell can be usedif it takes 30 joules to boil or almost boil the tissue, and a 150 msdwell can be used if it takes 18 joules to boil or almost boil thetissue. These values can may depend upon the surface area of the jaws ofthe device being used, or other factors.

Although the energy applied to the tissue can be a strong indicator ofthe amount of steam being created, the impedance of the tissue can alsoimpact the accuracy of the setting. For example, if the tissue has ahigher electrical impedance (such as fat), it can take more voltage andless current to boil the tissue, whereas if the tissue is veryconductive, the current does the work and creates large steam pocketswith the same amount of energy. Therefore, it can be desirable for asystem that uses energy application to determine a dwell time to alsodetermine and use the tissue impedance that the energy used to createthe boiling effect.

The control circuit can use other electrical characteristics todetermine a dwell time, including one or more of the following: current,reactance, inductance, impedance, resistance, power, phase angle, andenergy to check or improve a signal.

Steam is the result of the delivered current, which excites themolecules within the tissue and causes heating. When more current isrequired to heat the tissue, it suggests that more fluid is residingwithin the tissue, understanding that the tissue structure itself ismuch higher resistivity than the fluid content. Therefore, depending onthe function of the electrotherapeutic signal, e.g., how the signalapplies energy, it can be desirable for the control circuit to determinea peak current applied in the previous pulse, or the current deliveredas a function of time, or the total amount of current delivered in thatprevious pulse. The control circuit use the determined current and querya stored data set, such as a look up table, and determine or select adwell time based on the comparison.

For example, the control circuit, such as the control circuit 48 of FIG.2, can control and apply power to the tissue with current and voltagebeing allowed to float depending on the tissue impedance (this is asimplified explanation for general understanding). The control circuitcan determine the total amount of current applied in the previous pulse,such as by integrating the amount of current delivered, which can assistin understanding how much steam could have been created during an energyapplication. Current (I) is equal to the rate of change of the electriccharge (Q) with respect to time (I=dQ/dt). Therefore, the integral ofthe current I over a period of time is equal to the total amount ofelectric charge (Q) during that period of time.

Instead of using the total amount of energy delivered to the tissue, thepresent inventors have determined that the total amount of chargedelivered can be used to determine a dwell time. In some examples, thecontrol circuit can determine the dwell time as a ratio of the totalamount of charge or as a factor of the total amount of charge. In otherexamples, the control circuit can use the total amount of charge todetermine the dwell time using a stored data set, such as a look uptable, or by using some other mathematically derived calculation toprovide an appropriate dwell time that does not need to be the same forall energy pulses.

The dwell time can be further refined by including other factors, asdescribed above, or exclusions. An example of such an exclusion can beif the current was delivered over a period of time greater than 300 ms,then the control circuit can reduce the dwell time because the amount oftissue within the jaw may be having a significant impact. As such, thecontrol circuit can initiate a timer, compare the timer to a thresholdvalue, such as 300 ms, and determine a dwell time based on thecomparison. Alternatively, one or more feedback signals can be used,such as phase angle, to predict the composition of the tissue betweenthe energy conduction elements. The control circuit can then factor inthese feedback signals as indicators to determine an appropriate dwelltime.

Incremental Adjustment of Control Parameter as a Function of a MonitoredVariable

An initial transition of the collagen occurs at about 58 (±10) degreesCelsius (C.), where conformal changes occur to the collagen fibrils. Themain transition can occur at about 65 (±10) C, which corresponds to theprocess of gelatinization of collagen in a hydrated environment and iscaused by the breaking of internal cross-links. Other important andnotable temperatures bound tissue modification. At a general tissuetemperature of between about 90 -100 degrees C., additional phasechanges start to occur inside the tissue, the most notable being thewater converting to steam. This change is not desirable as the steam isresistive and although it drives energy robbing fluid out of the tissue,it also can damage surrounding tissues via its migration into adjacentstructures. This is not desirable as this damage can be uncontrolled andcan affect tissue outside of the jaw footprint.

From a clinical standpoint, this means that a surgeon should be mindfulof any potential “thermal spread” when using a device and activating itclose to a sensitive adjacent structure. This is not desirable and canlead to accidental tissue damage such as perforation and necrosis. Bothof which may be instant or worse still, occur many days after theapplication of energy.

Steam containing tissue is also more electrically resistant than thesame tissue with the water in a liquid state. This means that more ofthe energy that drives the tissue state change converts from current tovoltage. Because the current typically does the work of heating viamolecular excitation, it can be advantageous to limit the time in thesteam phase for good vessel sealing.

The present inventors have recognized the need for improved techniquesof power control (or voltage control) that attempts to maintain thepower output for longer in the advantageous state of collagentransition, before control is lost and bubble field generation occurs.Using various techniques described in detail below, an electrosurgicalgenerator, such as the electrosurgical generator 12 of FIG. 2, cancontrol an energy delivery of the therapeutic signal provided tobiological tissue during a portion of a therapeutic phase according toan incremental change in energy delivery as a function of a change in ameasured electrical parameter of the biological tissue.

Applying energy to tissue can generate steam. As the amount of steamincreases, the impedance increases. An increase in impedance can be anindication of steam generation. As the impedance increases, the currentdecreases and the voltage increases for the same amount of power beingdelivered (P=V*I). If, after the control circuit determines that steamis being generated, the control circuit continues to apply the sameamount of power, the steam generation can undesirably increase and canadversely affect adjacent tissue. However, by using various techniquesof this disclosure, the control circuit can monitor a change in anelectrical parameter, such a current or impedance, and reduce the power,for example, to keep the tissue in a state in which steam is justbeginning to be generated, but not generated in large amounts, which canbe desirable for affecting the collagen without undesirably creatingthermal margin.

A control circuit and a measurement circuit, such as the control circuit48 and the measurement circuit 46 of FIG. 2, can monitor the currentoutput of the generator and increases or decreases in the current can betranslated into corresponding increases or decreases in the outputpower. In some examples, the correlation between an increase in currentor a decrease in current and the subsequent control of increasing thepower or decreasing the power can be directly proportional.

In some examples, the control circuit can scale the power application soas to provide different powers depending on the change in the measuredelectrical parameter, such as current or impedance. The scaling can be afunction of the change in the measured electrical parameter of thebiological tissue. In some examples, the function can define a curve. Inother examples, the function can be a linear equation, such as a lineartranslation of the change in the value of the measured electricalparameter, such a current or impedance, to the change in power orvoltage, such as in watts or volts per second. The power (or voltage)can increase or decrease as the current changes. In some examples, thelinear equation can be monotonic. In some examples, one or both of aminimum value and a maximum value can be defined such that the controlcircuit can limit the change in power or voltage.

FIG. 23 is graph depicting an example of a relationship between a changein the value of a measured electrical parameter to a change in power.Although depicted specifically as a change in current per unit time to achange in power in watts per unit time, the techniques described are notlimited to current or power. In the example shown in FIG. 23, the y-axisof the graph 2100 can represent watts/second and the x-axis canrepresent the change in current/second.

In an example, the linear equation that defines the line 2102 caninclude an offset such that the line does not pass through the originsuch that when the change in current, or delta current value, is zerothe change in power is positive. For example, in the graph 2100 of achange in power versus a change in current, the line 2102 can have apositive slope and can extend through quadrants I, II, and III. Asanother example, in a graph of a change in voltage versus a change incurrent, the line can have a negative slope and can extend throughquadrants I, II, and IV. In the example shown in FIG. 23, one or both ofa maximum ramp rate 2104 and a minimum ramp rate 2106 can be definedsuch that the control circuit can limit the rate of change of power, forexample.

In an example, the relationships between the change in the measuredelectrical parameter and the incremental change in energy can be storedin a data set, such as a look up table. The control circuit can querythe stored data set, compare the change in the measured electricalparameter of the biological tissue to the stored data set, and determinethe incremental change in energy delivery based on the comparison.

Whether using the function, e.g., a linear function, or the stored dataset, the control circuit can monitor an electrical parameter, such as achange in current, so that the control circuit can make an adjustment inreal-time (or “on the fly”) to a controlling parameter, such as power orvoltage, to control an energy delivery of the therapeutic signalprovided to biological tissue during a portion of a therapeutic phase.In this manner, the control circuit can control the electrical power orvoltage of the therapeutic signal provided to the biological tissue as afunction of the change in the measured electrical parameter of thebiological tissue. For example, the control circuit can incrementallymodify the electrical power or voltage as a function of current.

By way of a non-limiting example, a small positive current rate changecan result in a medium power rate change. As another example, a zerocurrent rate change can result in a negative power rate change. Asanother example, a negative current rate change can result in a highnegative power rate change. As another example, a high current ratechange can result in a high power rate change. By monitoring the currentdelta (also referred to as a change in current), different powercontrols can be applied, which can drive different tissue results or bemodified to accommodate different application devices.

While applying power, the current can increase because the tissue is notyet boiling and, as the tissue is heated, it becomes more electricallyconductive. As such, more current is needed to increase the power. Usingvarious techniques of this disclosure, the control circuit, such thecontrol circuit 48 of FIG. 2, can permit the power to increase becausethe current is still increasing, which can desirably expedite the timeit takes for the collagen denaturizing. Eventually, a condition isreached in which the power cannot be applied to the tissue any fasterwithout tissue popping occurring. To avoid tissue popping, the controlcircuit can define a power (or voltage) maximum to limit the power (orvoltage) applied to the tissue.

As the amount of steam increases, the impedance increases. As theimpedance increases, the current decreases and the voltage increases forthe same amount of power delivered (P=V*I). If the control circuitdetermines that steam is being generated, the control circuit can dropthe power rapidly, but not so rapidly as to stop the steam from beinggenerated. As the impedance continues to increase, the control circuitcan determine the amount of energy delivered from the change inimpedance. Using the determined amount of energy delivered, the controlcircuit can stop applying power and pause momentarily to allow the steamto collapse.

The biological tissue includes salt and when energy is applied to thetissue, the sodium can burn. The burning sodium can become highlyconductive, which can skew the measurements used to determine whether toincrease or decrease the power or voltage. To avoid making a real-timedecision based on a minor, rapid change, such as burning sodium, theelectrosurgical generator, such as the electrosurgical generator 12 ofFIG. 2, can include or implement various filters. As an example, afilter can be added to the current sampling to smooth out the generatoroutput when considering the change in current delta. The frequency ofthe filtering can depend on the processing speed of the generatorcontrol CPU.

In some examples, the control circuit can further determine whether theproposed power (or voltage) increase or decrease should occur. Forexample, the control circuit can sample the recent increase or decreaseof the power (or voltage) and determine whether a continued increase (ordecrease) should be continued or whether the latest change in powerramping (or voltage ramping) is noise or within expected limits. Forexample, if the past two (or more) power ramp values (or voltage rampvalues) were positive and large, but the latest values indicate asignificant negative (decrease) in power, then the control circuit canoverride the decision to decrease the power (or voltage) untilsubsequent current delta calculations are evaluated.

In some examples, the control circuit can include boundaries for themaximum allowable change and/or maximum allowable output or ramp rate,thereby preventing the generator from being limited just by its hardwareor applying energy too quickly to the tissue. This can be achieved bylimiting the maximum power during the stage, limiting the maximum powerchange (e.g., limiting the maximum watts per second ramping rate), andthe like.

These power (or voltage) control techniques that can control an energydelivery of the therapeutic signal provided to biological tissue duringa portion of a therapeutic phase according to an incremental change inenergy delivery as a function of a change in a measured electricalparameter of the biological tissue can be used in a single rampingwaveform output, or in a pulsed waveform output. An advantage of apulsed waveform output is that the power increase quickly, if desired.For example, power can be significantly reduced (or temporarily stopped)under certain conditions to allow the steam to condense and power to besubsequently applied again in a ramping manner until a desired tissueeffect “end point” has been reached.

Aspects

To further illustrate the electrosurgical techniques described above, anon-limiting list of various aspects are described below. Each of thenon-limiting aspects may stand on its own, or may be combined in variouspermutations or combinations with one or more of the other aspects.

A. Short Circuit Error Trapping with Band Between Trigger and EscapeValues

Aspect A1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgical systemcomprising: a control circuit; and an output circuit coupled to thecontrol circuit and configured to deliver electrosurgical energy to anoutput terminal for delivery to a patient, the output terminalconfigured to couple to an electrosurgical device having two electrodes,wherein the control circuit is configured to: compare a first measuredimpedance value of biological tissue in electrical communication withthe two electrodes of the electrosurgical device to a first thresholdvalue; initiate a timer when the first measured impedance value is lessthan or equal to the first threshold value; compare a second measuredimpedance value of the tissue between the two electrodes to a secondthreshold value, wherein the second threshold value is greater than thefirst threshold value; and continue the delivery of electrosurgicalenergy when the second measured impedance value is less than the secondthreshold value and the timer has not met a time limit.

Aspect A2 can include or use or can optionally be combined with at leastsome features of Aspect A1 to include or use the control circuit beingconfigured to: reduce the delivery of electrosurgical energy when thesecond measured impedance value is less than the second threshold valueand the timer has met the time limit.

Aspect A3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects A1 or A2 to include or usethe control circuit being configured to: generate an indication when thetimer has met the time limit.

Aspect A4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects A1 through A3 to include oruse the timer being less than 6 seconds.

Aspect A5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects A1 through A4 to include oruse the control circuit configured to:

adjust at least one of the first threshold value, the second thresholdvalue, and the time limit based on at least one characteristic of theelectrosurgical device or based on at least one characteristic of anelectrosurgical generator configured to be coupled to theelectrosurgical device.

Aspect A6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects A1 through A5 to include oruse the at least one characteristic including a surface area of at leastone of the electrodes.

Aspect A7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects A1 through A6 to include oruse the electrodes being positioned on jaws of the electrosurgicaldevice, and where the at least one characteristic includes: a jaw forceof the electrosurgical device.

Aspect A8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects A1 through A7 to include oruse the at least one characteristic including an output current of theelectrosurgical generator.

Aspect A9 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects A1 through A8 to include oruse the electrodes being positioned on jaws of the electrosurgicaldevice, and the biological tissue being positioned between twoelectrodes of the electrosurgical device.

Aspect 10 can include or use a method of delivering electrical energy toan electrosurgical device, the method comprising: initiating an ongoingdelivery of electrosurgical energy to biological tissue in electricalcommunication with two electrodes of the electrosurgical device;comparing a first measured impedance value of the tissue to a firstthreshold value; initiating a timer when the first measured impedancevalue is less than or equal to the first threshold value; comparing asecond measured impedance value of the tissue to a second thresholdvalue, wherein the second threshold value is greater than the firstthreshold value; and continuing the delivery of electrosurgical energywhen the second measured impedance value is less than the secondthreshold value and the timer has not met a time limit.

Aspect A11 can include or use or can optionally be combined with atleast some features of Aspect A10 to include or use reducing thedelivery of electrosurgical energy when the second measured impedancevalue is less than the second threshold value and the timer has met thetime limit.

Aspect A12 can include or use or can optionally be combined with atleast some features of any one or more of Aspects A10 or A11 to includeor use generating an indication when the timer has met the time limit.

Aspect A13 can include or use or can optionally be combined with atleast some features of any one or more of Aspects A10 through A12 toinclude or use the electrodes being positioned on jaws of theelectrosurgical device, and the biological tissue being positionedbetween two electrodes of the electrosurgical device.

Aspect A14 can include or use or can optionally be combined with atleast some features of any one or more of Aspects A10 through A13, toinclude or use the timer being less than 6 seconds.

Aspect A15 can include or use or can optionally be combined with atleast some features of any one or more of Aspects A10 through A14 toinclude or use adjusting at least one of the first threshold value, thesecond threshold value, and the time limit based on at least onecharacteristic of the electrosurgical device or based on at least onecharacteristic of an electrosurgical generator configured to be coupledto the electrosurgical device.

Aspect A16 can include or use or can optionally be combined with atleast some features of any one or more of Aspects A10 through A15 toinclude or use the at least one characteristic of the electrosurgicaldevice including a surface area of at least one of the electrodes.

Aspect A17 can include or use or can optionally be combined with atleast some features of any one or more of Aspects A10 through A16 toinclude or use the electrodes being positioned on jaws of theelectrosurgical device, and the at least one characteristic of theelectrosurgical device including a jaw force of the electrosurgicaldevice.

Aspect A18 can include or use or can optionally be combined with atleast some features of any one or more of Aspects A10 through A17 toinclude or use the at least one characteristic of the electrosurgicalgenerator including an output current of the electrosurgical generator.

B. Open Circuit Check for Resistance Limit Endpoint RF Waveform andEvaluation of Open Circuit Time in End Phase

Aspect B1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgical systemcomprising: a control circuit; and an output circuit coupled to thecontrol circuit and configured to deliver electrosurgical energy to anoutput terminal for delivery to a patient, the output terminalconfigured to couple to an electrosurgical device having two jaws withcorresponding electrodes, wherein the control circuit is configured to:initiate a timer in response to a delivery of electrosurgical energy tobiological tissue in electrical communication with two electrodes of theelectrosurgical device; after the timer has met a time limit, compare arepresentation of impedance to a first threshold value; and continue thedelivery of electrosurgical energy when the representation of impedanceis less than the first threshold value.

Aspect B2 can include or use or can optionally be combined with at leastsome features of Aspect B1 to include or use the control circuitconfigured to: reduce the delivery of electrosurgical energy when therepresentation of impedance is greater than or equal to the firstthreshold value and less than a second threshold value.

Aspect B3 can include or use or can optionally be combined with at leastsome features of Aspects B1 or B2 to include or use the control circuitconfigured to: reduce the delivery of electrosurgical energy when therepresentation of impedance is greater than or equal to the secondthreshold value.

Aspect B4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects B1 through B3 to include oruse the control circuit configured to: generate an indication when therepresentation of impedance is greater than or equal to the secondthreshold value.

Aspect B5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects B1 through B4 to include oruse the control circuit configured to generate the indication when therepresentation of impedance is greater than or equal to the secondthreshold value is configured to: generate an audible indication.

Aspect B6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects B1 through B5 to include oruse the control circuit configured to generate the indication when therepresentation of impedance is greater than or equal to the secondthreshold value is configured to: generate a visual indication.

Aspect B7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects B1 through B6 to include oruse the representation of impedance including a value of the impedance.

Aspect B8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects B1 through B7 to include oruse the representation of impedance including a change in a value of theimpedance.

Aspect B9 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgical systemcomprising: a control circuit; and an output circuit coupled to thecontrol circuit and configured to deliver electrosurgical energy to anoutput terminal for delivery to a patient, the output terminalconfigured to couple to an electrosurgical device having two jaws withcorresponding electrodes, wherein the control circuit is configured to:initiate a timer in response to a delivery of electrosurgical energy tobiological tissue in electrical communication with two electrodes of theelectrosurgical device; after the timer has met a time limit, compare arate of change of impedance of the biological tissue to a firstthreshold value; and continue the delivery of electrosurgical energywhen the rate of change of impedance is less than the first thresholdvalue.

Aspect B10 can include or use or can optionally be combined with atleast some features of Aspect B9 to include or use the control circuitis configured to: reduce delivery of the energy when the rate of changeof impedance is greater than or equal to the first threshold value.

Aspect B11 can include or use or can optionally be combined with atleast some features of any one or more of Aspects B9 or B10 to includeor use the control circuit configured to: generate an indication whenthe rate of change of impedance is greater than or equal to the firstthreshold value.

Aspect B12 can include or use or can optionally be combined with atleast some features of any one or more of Aspects B9 through B11 toinclude or use the control circuit configured to generate the indicationwhen the rate of change of impedance is greater than or equal to thefirst threshold value is configured to: generate an indication.

Aspect B13 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a method ofdelivering electrical energy to an electrosurgical device, the methodcomprising: initiating a timer in response to a delivery ofelectrosurgical energy to biological tissue in electrical communicationwith two electrodes of the electrosurgical device; comparing arepresentation of impedance of the biological tissue to a thresholdvalue; continuing the delivery of electrosurgical energy until thethreshold value is met; upon reaching the threshold value, recording anelapsed time; and declaring an error state if the elapsed time is lessthan a time limit.

Aspect B14 can include or use or can optionally be combined with atleast some features of Aspect B13 to include or use determining adifference between first and second measured impedances and comparingthe determined difference to a predetermined delta impedance value; andin response to the determined difference being equal to or greater thanthe predetermined delta impedance value and the timer being less than athreshold time limit, generating an error signal.

Aspect B15 can include or use or can optionally be combined with atleast some features of any one or more of Aspects B13 or B14 to includeor use determining a difference between first and second measuredimpedances and comparing the determined difference to a predetermineddelta impedance value; and increasing a power ramp rate of theelectrosurgical energy in response to the comparison.

Aspect B16 can include or use or can optionally be combined with atleast some features of any one of or more of Aspects B13 through B15 toinclude or use continuing to increase the power ramp rate until eitherthe determined difference meets or exceeds the predetermined deltaimpedance value or a power limit is reached.

Aspect B17 can include or use or can optionally be combined with atleast some features of any one or more of Aspects B13 through B16 toinclude or use the power ramp rate being a first power ramp rate, and inresponse to reaching the power limit, adjusting the power ramp rate fromthe first power ramp to a second power ramp rate, wherein the secondpower ramp rate is slower than the first ramp rate.

Aspect B18 can include or use or can optionally be combined with atleast some features of any one or more of Aspects B13 through B17 toinclude or use the threshold value being a first threshold value, andduring a finishing phase: comparing the representation of impedance ofthe biological tissue to a second threshold value; and delivering theelectrosurgical energy at a constant power ramp rate until therepresentation of impedance meets or exceeds a second threshold value.

Aspect B19 can include or use or can optionally be combined with atleast some features of any one or more of Aspects B13 through B18 toinclude or use before the delivering the electrosurgical energy at theconstant power ramp rate, delivering the electrosurgical energy at aconstant power.

C. Alternate Power Correction Outputs in Low Accuracy Hardware Systems

Aspect C1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgical systemcomprising: a control circuit; and an output circuit coupled to thecontrol circuit and configured to deliver electrosurgical energy to anoutput terminal for delivery to a patient, the output terminalconfigured to couple to an electrosurgical device having two jaws withcorresponding electrodes, wherein the control circuit is configured to:compare a representation of an impedance of biological tissue inelectrical communication with two electrodes of the electrosurgicaldevice to a first threshold; select, from at least two powercorrections, a first power correction when the representation of theimpedance is within a first range; and apply the selected first powercorrection to a power setting of a power generator coupled theelectrosurgical device.

Aspect C2 can include or use or can optionally be combined with at leastsome features of Aspect C1 to include or use the control circuit beingconfigured to select, from the at least two power corrections, a secondpower correction when the representation of the impedance is within asecond range.

Aspect C3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects C1 or C2 to include or usethe control circuit being configured to compare a representation of atleast one secondary parameter to at least one threshold; and select,from the at least two power corrections, a third power correction whenthe representation of the at least one secondary parameter is less thanthe at least one threshold.

Aspect C4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects C1 through C3 to include oruse the at least one secondary parameter including one or more of anoutput current of the power generator, a tissue temperature, and a phaseangle.

Aspect C5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects C1 through C4 to include oruse the control circuit being configured to: using the corrected powersetting, deliver electrosurgical energy via the electrodes of theelectrosurgical device during a period of time.

Aspect C6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects C1 through C5 to include oruse the period of time being based at least on a range of impedancevalues.

Aspect C7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects C1 through C6 to include oruse the period of time being based at least on an amount of deliveredelectrosurgical energy.

Aspect C8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects C1 through C7 to include oruse the control circuit being configured to: using the corrected powersetting, deliver electrosurgical energy via the electrodes of theelectrosurgical device; and reduce the application of the selected firstpower correction to the power setting when the representation ofimpedance meets or exceeds a second threshold.

Aspect C9 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects C1 through C8 to include oruse: using the corrected power setting, deliver electrosurgical energyvia the electrodes of the electrosurgical device; and dynamically adjustat least one of an upper limit and a lower limit of the first range whenthe representation of the impedance is within a predetermined percentageor value of the upper or lower limit.

Aspect C10 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a method ofdelivering electrical energy to an electrosurgical device, the methodcomprising: comparing a representation of an impedance of a biologicaltissue in electrical communication with two electrodes of theelectrosurgical device to a first threshold; selecting, from at leasttwo power corrections, a first power correction when the representationof the impedance is within a first range; and applying the selectedfirst power correction to a power setting of a power generator coupledthe electrosurgical device.

Aspect C11 can include or use or can optionally be combined with atleast some features of Aspect C10 to include or use selecting, from theat least two power corrections, a second power correction when therepresentation of the impedance is within a second range.

Aspect C12 can include or use or can optionally be combined with atleast some features of any one or more of Aspects C10 or C11 to includeor use comparing a representation of at least one secondary parameter toat least one threshold; and selecting, from the at least two powercorrections, a third power correction when the representation of the atleast one secondary parameter is less than the at least one threshold.

Aspect C13 can include or use or can optionally be combined with atleast some features of any one or more of Aspects C10 through C12 toinclude or use the at least one secondary parameter including one ormore of an output current of the power generator, a tissue temperature,and a phase angle.

Aspect C14 can include or use or can optionally be combined with atleast some features of any one or more of Aspects C10 through C13 toinclude or use: using the corrected power setting, deliveringelectrosurgical energy via the electrodes of the electrosurgical deviceduring a period of time.

Aspect C15 can include or use or can optionally be combined with atleast some features of any one or more of Aspects C10 through C14 toinclude or use the period of time being based at least on a range ofimpedance values.

Aspect C16 can include or use or can optionally be combined with atleast some features of any one or more of Aspects C10 through C15 toinclude or use the period of time being based at least on an amount ofdelivered electrosurgical energy.

Aspect C17 can include or use or can optionally be combined with atleast some features of any one or more of Aspects C10 through C16 toinclude or use: using the corrected power setting, deliveringelectrosurgical energy via the electrodes of the electrosurgical device;and reducing the application of the selected first power correction tothe power setting when the representation of impedance meets or exceedsa second threshold.

Aspect C18 can include or use or can optionally be combined with atleast some features of any one or more of Aspects C10 through C17 toinclude or use: using the corrected power setting, deliveringelectrosurgical energy via the electrodes of the electrosurgical device;and applying a second power correction to the power setting when therepresentation of the impedance is a specified percentage above an upperlimit of the first range.

D. Reduced Thermal Margin Combination Energy Device

Aspect D1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a combinationultrasonic energy and electrosurgical energy system comprising a controlcircuit; and an output circuit coupled to the control circuit andconfigured to deliver energy to an output terminal for delivery to apatient, the output terminal configured to couple to an electrosurgicaldevice having two jaws with corresponding electrodes, wherein thedelivered energy includes at least some ultrasonic energy, wherein thecontrol circuit is configured to: control the delivery of energy tobiological tissue in electrical communication with two electrodes of theelectrosurgical device; measure a representation of a tissue parameterof the biological tissue; and reduce a level of or terminate thedelivery of energy based on a characteristic of the measuredrepresentation of the tissue parameter of the biological tissue, whereinthe delivered energy is a combination of electrosurgical energy andultrasonic energy, and wherein the control circuit configured to reducethe level of or terminate the delivery of energy is configured to:reduce the level of the ultrasonic energy.

Aspect D2 can include or use or can optionally be combined with at leastsome features of Aspect D1 to include or use the control circuit beingconfigured to reduce the level of the ultrasonic energy is configuredto: terminate the delivery of the ultrasonic energy.

Aspect D3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects D1 or D2 to include or usethe control circuit being configured to: reduce the level of theelectrosurgical energy.

Aspect D4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects D1 through D3 to include oruse the control circuit being configured to reduce the level of theelectrosurgical energy being further configured to: terminate thedelivery of the electrosurgical energy.

Aspect D5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects D1 through D4 to include oruse the delivered energy being a combination of electrosurgical energyand ultrasonic energy, and the electrosurgical energy beingpower-controlled.

Aspect D6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects D1 through D5 to include oruse the delivered energy being a combination of electrosurgical energyand ultrasonic energy, and the electrosurgical energy beingvoltage-controlled.

Aspect D7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects D1 through D6 to include oruse the measured representation of the tissue parameter being animpedance value, and the control circuit being configured to: comparethe impedance value to a threshold value; and reduce the level of theultrasonic energy based on the comparison.

Aspect D8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects D1 through D7 to include oruse the measured representation of the tissue parameter being a changein impedance, the method comprising: compare the change in impedance toa threshold value; and reduce the level of the ultrasonic energy basedon the comparison.

Aspect D9 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a method ofdelivering energy to a combination ultrasonic energy and electrosurgicalenergy device, the method comprising: delivering energy to a biologicaltissue in electrical communication with two electrodes of anelectrosurgical device, wherein the delivered energy includes at leastsome ultrasonic energy; measuring a representation of a tissue parameterof the biological tissue; and reducing a level of or terminating thedelivery of the energy based upon a characteristic of the measuredrepresentation of the tissue parameter, wherein the delivered energy isa combination of electrosurgical energy and ultrasonic energy, andwherein reducing the level of or terminating the delivery of energyincludes: reducing the level of the ultrasonic energy.

Aspect D10 can include or use or can optionally be combined with atleast some features of Aspect D9 to include or use reducing the level ofthe ultrasonic energy including terminating the delivery of theultrasonic energy.

Aspect D11 can include or use or can optionally be combined with atleast some features of any one or more of Aspects D9 or D10 to includeor use reducing the level of the electrosurgical energy.

Aspect D12 can include or use or can optionally be combined with atleast some features of any one or more of Aspects D9 through D11 toinclude or use reducing the level of the electrosurgical energyincluding terminating the delivery of the electrosurgical energy.

Aspect D13 can include or use or can optionally be combined with atleast some features of any one or more of Aspects D9 through D12 toinclude or use the delivered energy being a combination ofelectrosurgical energy and ultrasonic energy, and the electrosurgicalenergy being power-controlled.

Aspect D14 can include or use or can optionally be combined with atleast some features of any one or more of Aspects D9 through D13 toinclude or use the delivered energy being a combination ofelectrosurgical energy and ultrasonic energy, and the electrosurgicalenergy being voltage-controlled.

Aspect D15 can include or use or can optionally be combined with atleast some features of any one or more of Aspects D9 through D14 toinclude or use the measured representation of the tissue parameter beingan impedance value, the method comprising: comparing the impedance valueto a threshold value; and reducing the level of the ultrasonic energybased on the comparison.

Aspect D16 can include or use or can optionally be combined with atleast some features of any one or more of Aspects D9 through D15 toinclude or use the measured representation of the tissue parameter beinga change in impedance, the method comprising: comparing the change inimpedance to a threshold value; and reducing the level of the ultrasonicenergy based on the comparison.

E. Staged Resistance Values to Control Thermal Margins in Systems withSlow CPUs

Aspect E1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgical systemcomprising: a control circuit; and an output circuit coupled to thecontrol circuit and configured to deliver energy to an output terminalfor delivery to a patient, the output terminal configured to couple toan electrosurgical device with at least one electrode, wherein thecontrol circuit is configured to: count and deliver electrosurgicalenergy pulses to biological tissue in communication with the at leastone electrode; and for a plurality of electrosurgical energy pulses:compare a parameter to a threshold value; and adjust the threshold valuebased on the count of the electrosurgical energy pulse.

Aspect E2 can include or use or can optionally be combined with at leastsome features of Aspect E1 to include or use the parameter beingselected from the group consisting of: an impedance of the biologicaltissue, a change in impedance of the biological tissue, a rate of changeof the impedance of the biological tissue, a change in a phase angle, achange in a current of the delivered electrosurgical energy pulse, and achange in an output voltage of the delivered electrosurgical energypulse.

Aspect E3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects E1 or E2 to include or usethe control circuit being configured to: retrieve data representing thethreshold value from a memory device.

Aspect E4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects E1 through E3 to include oruse the control circuit being configured to: compare a first measuredparameter to a second measured parameter, and wherein the controlcircuit configured to adjust the threshold value based on the count ofthe electrosurgical energy pulse is configured to: adjust the thresholdvalue based on a difference between the first measured parameter and thesecond measured parameter.

Aspect E5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects E1 through E4 to include oruse the control circuit being configured to: compare a first measuredparameter to a second measured parameter, and wherein the controlcircuit configured to adjust the threshold value based on the count ofthe electrosurgical energy pulse is configured to: adjust the thresholdvalue based on the first measured parameter being greater than thesecond measured parameter.

Aspect E6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects E1 through E5 to include oruse the control circuit being configured to: compare a first measuredparameter to a second measured parameter, and wherein the controlcircuit configured to adjust the threshold value based on the count ofthe electrosurgical energy pulse is configured to: adjust the thresholdvalue based on the first measured parameter being less than the secondmeasured parameter.

Aspect E7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects E1 through E6 to include oruse the control circuit being configured to: determine a rate of changebetween a first measured parameter and a second measured parameter, andwherein the control circuit is configured to adjust the threshold valuebased on the count of the electrosurgical energy pulse is configured to:adjust the threshold value based on the rate of change between the firstmeasured parameter and a second measured parameter.

Aspect E8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects E1 through E7 to include oruse the control circuit being configured to: adjust the threshold valuebased on the parameter.

Aspect E9 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects E1 through E8 to include oruse the control circuit being configured to: reduce the delivery of theplurality of electrosurgical energy pulses when a measuredrepresentation of impedance meets or exceeds an endpoint value.

Aspect E10 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgical systemcomprising: a control circuit; and an output circuit coupled to thecontrol circuit and configured to deliver energy to an output terminalfor delivery to a patient, the output terminal configured to couple toan electrosurgical device having two jaws with corresponding electrodes,wherein the control circuit is configured to: count and deliverelectrosurgical energy pulses to biological tissue in electricalcommunication with two electrodes of the surgical device; and for aplurality of electrosurgical energy pulses: deliver a firstelectrosurgical energy pulse to biological tissue in electricalcommunication with two electrodes of the electrosurgical device; comparea first measured representation of impedance of the biological tissue toa first threshold value; reduce delivery of the first electrosurgicalenergy pulse when the first measured representation of impedance meetsor exceeds the first threshold value; increase the first threshold valueto a second threshold value based on the count of the pulse; deliver asecond electrosurgical energy pulse to the tissue; compare a secondmeasured representation of impedance of the tissue to the secondthreshold value; and reduce delivery of the second electrosurgicalenergy pulse when the second measured representation of impedance meetsor exceeds the second threshold value.

Aspect E11 can include or use or can optionally be combined with atleast some features of Aspect E10 to include or use the control circuitbeing configured to: retrieve data representing the first and secondthreshold values from a memory device.

Aspect E12 can include or use or can optionally be combined with atleast some features of any one or more of Aspects E10 or E11 to includeor use the control circuit being configured to: compare the firstmeasured representation of impedance to the second measuredrepresentation of impedance; and determine the second threshold valuebased on a difference between the first measured representation ofimpedance and the second measured representation of impedance.

Aspect E13 can include or use or can optionally be combined with atleast some features of any one or more of Aspects E10 through E12 toinclude or use the control circuit being configured to: compare thefirst measured representation of impedance to the second measuredrepresentation of impedance; and determine the second threshold valuebased on the first measured representation of impedance being greaterthan the second measured representation of impedance.

Aspect E14 can include or use or can optionally be combined with atleast some features of any one or more of Aspects E10 through E13 toinclude or use the control circuit being configured to: compare thefirst measured representation of impedance to the second measuredrepresentation of impedance; and determine the second threshold valuebased on the first measured representation of impedance being less thanthe second measured representation of impedance.

Aspect E15 can include or use or can optionally be combined with atleast some features of any one or more of Aspects E10 through E14 toinclude or use the control circuit being configured to: determine a rateof change between the first measured representation of impedance and thesecond measured representation of impedance; and determine the secondthreshold value based on the rate of change.

Aspect E16 can include or use or can optionally be combined with atleast some features of any one or more of Aspects E10 through E15 toinclude or use the control circuit being configured to: determine thesecond threshold value based on the first measured representation ofimpedance.

Aspect E17 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a method ofdelivering electrical energy to an electrosurgical device, the methodcomprising: counting and delivering a plurality of electrosurgicalenergy pulses to biological tissue in electrical communication with twoelectrodes of the electrosurgical device; for a plurality ofelectrosurgical energy pulses: comparing a parameter to a thresholdvalue; and adjusting the threshold value based on the count of theelectrosurgical energy pulses.

Aspect E18 can include or use or can optionally be combined with atleast some features of Aspect E17 to include or use the parameter beingselected from the group consisting of: an impedance of the biologicaltissue, a change in impedance of the biological tissue, a rate of changeof the impedance of the biological tissue, a change in a phase angle, achange in a current of the delivered electrosurgical energy pulse, and achange in an output voltage of the delivered electrosurgical energypulse.

Aspect E19 can include or use or can optionally be combined with atleast some features of any one or more of Aspects E17 or E18 to includeor use retrieving data representing the threshold value from a memorydevice.

Aspect E20 can include or use or can optionally be combined with atleast some features of any one or more of Aspects E17 through E19 toinclude or use comparing a first measured parameter to a second measuredparameter, wherein adjusting the threshold value based on the count ofthe electrosurgical energy pulse includes: adjusting the threshold valuebased on a difference between the first measured parameter and thesecond measured parameter.

Aspect E21 can include or use or can optionally be combined with atleast some features of any one or more of Aspects E17 through E20 toinclude or use comparing a first measured parameter to a second measuredparameter, wherein adjusting the threshold value based on the count ofthe electrosurgical energy pulse includes: adjusting the threshold valuebased on the first measured parameter being greater than the secondmeasured parameter.

Aspect E22 can include or use or can optionally be combined with atleast some features of any one or more of Aspects E17 through E21 toinclude or use comparing a first measured parameter to a second measuredparameter, wherein adjusting the threshold value based on the count ofthe electrosurgical energy pulse includes: adjusting the threshold valuebased on the first measured parameter being less than the secondmeasured parameter.

Aspect E23 can include or use or can optionally be combined with atleast some features of any one or more of Aspects E17 through E22 toinclude or use determining a rate of change between a first measuredparameter and a second measured parameter, wherein adjusting thethreshold value based on the count of the electrosurgical energy pulseincludes: adjusting the threshold value based on the rate of changebetween the first measured parameter and a second measured parameter.

Aspect E24 can include or use or can optionally be combined with atleast some features of any one or more of Aspects E17 through E23 toinclude or use adjusting the threshold value based on the parameter.

Aspect E25 can include or use or can optionally be combined with atleast some features of any one or more of Aspects E17 through E24 toinclude or use reducing the delivery of the plurality of electrosurgicalenergy pulses when a measured representation of impedance meets orexceeds an endpoint value.

F. Power-Controlled Waveform

Aspect F1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgicalgenerator configured to generate and provide controlled electrical powerof a therapeutic signal to biological tissue in electrical communicationwith an instrument, the surgical generator comprising: a control circuitin communication with an electrical-energy source, the electrical-energysource electrically coupled to the instrument and configured to generatethe therapeutic signal, the control circuit configured to: control theelectrical power of the therapeutic signal provided to the biologicaltissue during a portion of a therapeutic phase according to atherapeutic plan.

Aspect F2 can include or use or can optionally be combined with at leastsome features of Aspect F1 to include or use the control circuit beingconfigured to control a voltage of the therapeutic signal provided tothe biological tissue during a portion of a drying phase according tothe therapeutic plan.

Aspect F3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects F1 or F2 to include or usethe control circuit being configured to: monitor the voltage of thetherapeutic signal; and maintain the voltage when the voltage meets avoltage threshold.

Aspect F4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects F1 through F3 to include oruse the control circuit being configured to: control the electricalpower of the therapeutic signal provided to the biological tissue duringthe portion of the therapeutic phase using a pre-defined power curve.

Aspect F5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects F1 through F4 to include oruse the pre-defined power curve including a linear portion.

Aspect F6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects F1 through F5 to include oruse the pre-defined power curve including two or more linear portions.

Aspect F7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects F1 through F6 to include oruse the control circuit configured to control the electrical power ofthe therapeutic signal provided to the biological tissue beingconfigured to: incrementally modify the electrical power as a functionof current.

Aspect F8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects F1 through F7 to include oruse the function of current being a function of an instantaneousmeasured change in current.

Aspect F9 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects F1 through F8 to include oruse the control circuit configured to control the electrical power ofthe therapeutic signal provided to the biological tissue beingconfigured to: incrementally modify the electrical power as a functionof resistance.

Aspect F10 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a method ofdelivering controlled electrical power of a therapeutic signal tobiological tissue in electrical communication with an instrument, themethod comprising: generating, using an electrical-energy sourceelectrically coupled to the instrument, the therapeutic signal; andcontrolling the electrical power of the therapeutic signal provided tothe biological tissue during a portion of the therapeutic phaseaccording to a therapeutic plan.

Aspect F11 can include or use or can optionally be combined with atleast some features of Aspect F10 to include or use controlling avoltage of the therapeutic signal provided to the biological tissueduring a portion of a drying phase according to the therapeutic plan.

Aspect F12 can include or use or can optionally be combined with atleast some features of any one or more of Aspects F10 or F 11 to includeor use monitoring the voltage of the therapeutic signal; and maintainingthe voltage when the voltage meets a voltage threshold.

Aspect F13 can include or use or can optionally be combined with atleast some features of any one or more of Aspects F10 through F12 toinclude or use controlling the electrical power of the therapeuticsignal provided to the biological tissue during the portion of thetherapeutic phase using a pre-defined power curve.

Aspect F14 can include or use or can optionally be combined with atleast some features of any one or more of Aspects F10 through F13 toinclude or use the pre-defined power curve including a linear portion.

Aspect F15 can include or use or can optionally be combined with atleast some features of any one or more of Aspects F10 through F14 toinclude or use the pre-defined power curve including two or more linearportions.

Aspect F16 can include or use or can optionally be combined with atleast some features of any one or more of Aspects F10 through F15 toinclude or use incrementally modifying the electrical power as afunction of current.

Aspect F17 can include or use or can optionally be combined with atleast some features of any one or more of Aspects F10 through F16 toinclude or use the function of current being a function of aninstantaneous measured change in current.

Aspect F18 can include or use or can optionally be combined with atleast some features of any one or more of Aspects F10 through F17 toinclude or use the function of the instantaneous measured change incurrent being a linear function.

Aspect F19 can include or use or can optionally be combined with atleast some features of any one or more of Aspects F10 through F18 toinclude or use incrementally modifying the electrical power as afunction of resistance.

G. Incremental Adjustment of Control Parameter as a Function of aMonitored Variable

Aspect G1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgicalgenerator configured to generate and provide controlled electrical powerof a therapeutic signal to biological tissue in electrical communicationwith an instrument, the surgical generator comprising: a control circuitin communication with an electrical-energy source, the electrical-energysource electrically coupled to the instrument and configured to generatethe therapeutic signal, the control circuit configured to: control anenergy delivery of the therapeutic signal provided to the biologicaltissue during a portion of a therapeutic phase according to anincremental change in energy delivery as a function of a change in ameasured electrical parameter of the biological tissue.

Aspect G2 can include or use or can optionally be combined with at leastsome features of Aspect G1 to include or use the control circuitconfigured to control the energy deliver of the therapeutic signal beingconfigured to: control the electrical power of the therapeutic signalprovided to the biological tissue.

Aspect G3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects G1 or G2 to include or usethe control circuit configured to control the electrical power of thetherapeutic signal provided to the biological tissue being configuredto: incrementally modify the electrical power as a function of current.

Aspect G4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects G1 through G3 to include oruse the control circuit configured to control the energy deliver of thetherapeutic signal being configured to: control a voltage of thetherapeutic signal provided to the biological tissue.

Aspect G5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects G1 through G4 to include oruse the control circuit configured to control the electrical power ofthe therapeutic signal provided to the biological tissue beingconfigured to: incrementally modify the voltage as a function ofcurrent.

Aspect G6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects G1 through G5 to include oruse the measured electrical parameter including a change in impedance.

Aspect G7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects G1 through G6 to include oruse the measured electrical parameter including a change in current.

Aspect G8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects G1 through G7 to include oruse the control circuit being configured to: compare the change in themeasured electrical parameter of the biological tissue to a stored dataset; and determine the incremental change in energy delivery based onthe comparison.

H. Terminating Drying Cycles by Monitoring Impedance

Aspect H1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgicalgenerator configured to generate and provide controlled electrical powerof a therapeutic signal to biological tissue in electrical communicationwith a surgical instrument, the surgical generator comprising: ameasurement circuit coupled to a control circuit and configured tomeasure an impedance of the biological tissue during a therapeuticphase; the control circuit in communication with an electrical-energysource, the electrical-energy source electrically coupled to theinstrument and configured to generate the therapeutic signal, thecontrol circuit configured to: control an energy delivery of thetherapeutic signal provided to the biological tissue during atherapeutic phase; and in response to the measured impedance changing bya predetermined delta impedance value, reduce the energy delivery duringthe therapeutic phase, wherein the predetermined delta impedance is achange in impedance relative to a minimum impedance measurement during apulse of the therapeutic signal.

Aspect H2 can include or use or can optionally be combined with at leastsome features of Aspect H1 to include or use the control circuit beingconfigured to: control an electrical power of the therapeutic signalprovided to the biological tissue.

Aspect H3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects H1 or H2 to include or usethe control circuit being configured to: control a voltage of thetherapeutic signal provided to the biological tissue.

Aspect H4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects H1 through H3 to include oruse the control circuit being configured to: monitor the voltage of thetherapeutic signal; and maintain the voltage when the voltage meets avoltage threshold.

Aspect H5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects H1 through H4 to include oruse the therapeutic phase being a drying phase.

Aspect H6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects H1 through H5 to include oruse the measurement circuit being configured to: measure a firstimpedance conducted by the biological tissue and measure a secondimpedance conducted by the biological tissue during the drying phase;wherein the control circuit is configured to: control theelectrical-energy source to provide a drying signal to the biologicaltissue during the drying phase; and reduce the drying phase in responseto a comparison between first impedance and the second impedanceindicating a phase change of liquid in the biological tissue.

Aspect H7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects H1 through H6 to include oruse the control circuit being configured to control the drying signalaccording to a drying schedule.

Aspect H8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects H1 through H7 to include oruse the measurement circuit being configured to measure the impedanceconducted by the biological tissue during the drying phase.

Aspect H9 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects H1 through H8 to include oruse the control circuit being configured to: compare the measuredimpedance to the minimum impedance measurement; and store the measuredimpedance as the minimum impedance measurement when the measuredimpedance is less than the minimum impedance measurement.

Aspect H10 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgicalgenerator configured to generate and provide controlled electrical powerof a therapeutic signal to biological tissue in electrical communicationwith a surgical instrument, the surgical generator comprising: ameasurement circuit coupled to a control circuit and configured tomeasure an impedance of the biological tissue during a therapeuticphase; the control circuit in communication with an electrical-energysource, the electrical-energy source electrically coupled to theinstrument and configured to generate the therapeutic signal, thecontrol circuit configured to: control an energy delivery of thetherapeutic signal provided to the biological tissue during atherapeutic phase; and in response to the measured impedance changing bya predetermined delta impedance value, reduce the energy delivery duringthe therapeutic phase, wherein the predetermined delta impedance is achange in impedance relative to an impedance measurement taken at a settime interval after the therapeutic phase has begun.

I. Terminating Drying Cycles by Monitoring Current, and Current in OnePhase and Impedance in One Phase

Aspect I1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgicalgenerator configured to generate and provide controlled electrical powerof a therapeutic signal to biological tissue in electrical communicationwith a surgical instrument, the surgical generator comprising: ameasurement circuit coupled to a control circuit and configured tomeasure a current provided to the biological tissue during a therapeuticphase; the control circuit in communication with an electrical-energysource, the electrical-energy source electrically coupled to theinstrument and configured to generate the therapeutic signal, thecontrol circuit configured to: control an energy delivery of thetherapeutic signal provided to the biological tissue during atherapeutic phase; and in response to the measured electrical current ofthe biological tissue satisfying a predetermined value, reduce theenergy delivery during the therapeutic phase.

Aspect I2 can include or use or can optionally be combined with at leastsome features of Aspect C10 to include or use the predetermined valuebeing an absolute current threshold value.

Aspect I3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects I1 or I2 to include or usethe predetermined value is a change in current relative to an initialcurrent measurement.

Aspect I4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects I1 through I3 to include oruse the predetermined value being a change in current relative to amaximum current measurement during a pulse of the therapeutic signal.

Aspect I5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects I1 through I4 to include oruse the control circuit being configured to: control an electrical powerof the therapeutic signal provided to the biological tissue.

Aspect I6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects I1 through I5 to include oruse the control circuit being configured to control a voltage of thetherapeutic signal provided to the biological tissue.

Aspect I7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects I1 through I6 to include oruse the therapeutic phase being a drying phase.

Aspect I8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects I1 through I7 to include oruse the measurement circuit being configured to: measure a firstelectrical current conducted by the biological tissue and measure asecond electrical current conducted by the biological tissue during thedrying phase; and wherein the control circuit is configured to controlthe electrical-energy source to provide a drying signal to thebiological tissue during the drying phase; and reduce the drying signalin response to a ratio of the measured first electrical current to themeasured second electrical current exceeding a predetermined factorindicating a phase change of liquid in the biological tissue.

Aspect I9 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects I1 through I8 to include oruse the control circuit being configured to control the drying signalaccording to a drying schedule.

Aspect I10 can include or use or can optionally be combined with atleast some features of any one or more of Aspects I1 through I9 toinclude or use the drying schedule being a monotonically-increasingelectrical-power schedule.

Aspect I11 can include or use or can optionally be combined with atleast some features of any one or more of Aspects I1 through I10 toinclude or use the measurement circuit being configured to measureelectrical current conducted by the biological tissue during the dryingphase.

Aspect I12 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgicalgenerator configured to generate and provide controlled electrical powerof a therapeutic signal to biological tissue in electrical communicationwith a surgical instrument, the surgical generator comprising: ameasurement circuit coupled to a control circuit and configured tomeasure first and second electrical parameters of the biological tissueduring first and second pulses, respectively, of the plurality oftherapeutic pulses; the control circuit in communication with anelectrical-energy source, the electrical-energy source electricallycoupled to the instrument and configured to generate the therapeuticsignal, the control circuit configured to: control an energy delivery ofthe therapeutic signal provided to the biological tissue during aplurality of therapeutic pulses; in response to the measured firstelectrical parameter of the biological tissue meeting a first thresholdvalue, modify the energy delivery during the first pulse; and inresponse to the measured second parameter of the biological tissuemeeting a second threshold value, modify the energy delivery during thesecond pulse.

Aspect I13 can include or use or can optionally be combined with atleast some features of Aspect I12 to include or use the first phasebeing during a drying phase.

Aspect I14 can include or use or can optionally be combined with atleast some features of any one or more of Aspects I12 or I13 to includeor use the first parameter being a current, and wherein the firstthreshold value is a change in current relative to an initial currentmeasurement.

Aspect I15 can include or use or can optionally be combined with atleast some features of any one or more of Aspects I12 through I14 toinclude or use the first parameter being a current, and wherein thefirst threshold value is a change in current relative to a maximumcurrent measurement during the first pulse.

Aspect I16 can include or use or can optionally be combined with atleast some features of any one or more of Aspects I12 through I15 toinclude or use the second phase being a sealing phase.

Aspect I17 can include or use or can optionally be combined with atleast some features of any one or more of Aspects I12 through I16 toinclude or use the second parameter being an impedance.

Aspect I18 can include or use or can optionally be combined with atleast some features of any one or more of Aspects I12 through I17 toinclude or use the control circuit being configured to control anelectrical power of the therapeutic signal provided to the biologicaltissue.

Aspect I19 can include or use or can optionally be combined with atleast some features of any one or more of Aspects I12 through I18 toinclude or use the control circuit being configured to control a voltageof the therapeutic signal provided to the biological tissue.

J. Evaluation of Consumed Energy

Aspect J1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgicalgenerator configured to generate and provide a therapeutic signal tobiological tissue in electrical communication with a surgicalinstrument, the surgical generator comprising: a control circuit incommunication with an electrical-energy source, the electrical-energysource electrically coupled to the instrument and configured to generatethe therapeutic signal, the control circuit configured to: control anenergy delivery of the therapeutic signal provided to the biologicaltissue during at least one of an interrogation phase and a first dryingphase; after completion of at least the first drying phase, compare anamount of energy delivered to the biological tissue during the at leastone of the interrogation and the first drying phase to a thresholdenergy value; and adjust delivery of the therapeutic signal based on thecomparison.

Aspect J2 can include or use or can optionally be combined with at leastsome features of Aspect J1 to include or use the control circuit beingconfigured to control an electrical power of the therapeutic signalprovided to the biological tissue.

Aspect J3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects J1 or J2 to include or usethe control circuit being configured to control a voltage of thetherapeutic signal provided to the biological tissue.

Aspect J4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects J1 through J3 to include oruse the control circuit configured to adjust delivery of the therapeuticsignal based on the comparison being configured to control the energydelivery of the therapeutic signal provided to the biological tissueduring a second drying phase if the amount of energy delivered exceedsthe threshold energy value.

Aspect J5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects J1 through J4 to include oruse the control circuit configured to adjust delivery of the therapeuticsignal based on the comparison being configured to: control the energydelivery of the therapeutic signal provided to the biological tissueduring a finishing phase if the amount of energy delivered is less thanthe threshold energy value.

Aspect J6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects J1 through J5 to include oruse a measurement circuit coupled to the control circuit and configuredto measure an impedance of the biological tissue; wherein the controlcircuit is configured to: determine a power ramp rate for delivery ofthe therapeutic signal based on the measured impedance.

Aspect J7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects J1 through J6 to include oruse the control circuit being configured to: determine a differencebetween first and second measured impedances; and adjust the power ramprate in response to the determined difference being less than apredetermined delta impedance value.

Aspect J8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects J1 through J7 to include oruse the control circuit configured to adjust the power ramp rate inresponse to the determined difference being less than the predetermineddelta impedance value being configured to increase the power ramp rateuntil either the determined difference is equal to or greater than thepredetermined delta impedance value or the amount of energy delivered isequal to or greater than the threshold energy value.

Aspect J9 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects J1 through J8 to include oruse a measurement circuit coupled to the control circuit and configuredto measure an impedance of the biological tissue; wherein the controlcircuit is configured to: during a finishing phase: initiate a timer;determine a difference between measured impedances and compare thedetermined difference to a predetermined delta impedance value; inresponse to the determined difference being equal to or greater than thepredetermined delta impedance value and the timer being greater than athreshold time limit, generate an error signal.

Aspect J10 can include or use or can optionally be combined with atleast some features of any one or more of Aspects J1 through J9 toinclude or use the error signal being an open circuit error signal.

Aspect J11 can include or use or can optionally be combined with atleast some features of any one or more of Aspects J1 through J10 toinclude or use the control circuit configured to adjust delivery of thetherapeutic signal based on the comparison being configured to repeat adrying phase.

Aspect J12 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgicalgenerator configured to generate and provide a therapeutic signal tobiological tissue in electrical communication with a surgicalinstrument, the surgical generator comprising: a control circuit incommunication with an electrical-energy source, the electrical-energysource electrically coupled to the instrument and configured to generatethe therapeutic signal, the control circuit configured to: control anenergy delivery of the therapeutic signal provided to the biologicaltissue during at least one of an interrogation phase and a first dryingphase; after completion of at least the first drying phase, compare anamount of current delivered to the biological tissue during the at leastone of the interrogation and the first drying phase to a thresholdenergy value; and adjust delivery of the therapeutic signal based on thecomparison.

K. Phase Angle Measurement

Aspect K1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use an electrosurgicalgenerator configured to generate and provide a therapeutic signal tobiological tissue in electrical communication with a surgicalinstrument, the surgical generator comprising: a measurement circuitcoupled to a control circuit and configured to measure a referenceimpedance angle of the biological tissue during an interrogation phase;and the control circuit in communication with an electrical-energysource, the electrical-energy source electrically coupled to theinstrument and configured to generate the therapeutic signal, thecontrol circuit configured to: control delivery of the therapeuticsignal provided to the biological tissue; compare the measured referenceimpedance angle with an angle threshold; and generate a responseindicative of an environmental condition of the instrument based on thecomparison of the measured reference impedance angle with the anglethreshold.

Aspect K2 can include or use or can optionally be combined with at leastsome features of Aspect K1 to include or use the measured referenceimpedance angle is substantially equal to an angular difference betweena voltage across and current conducted by the biological tissue asmeasured by the measurement circuit.

Aspect K3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects K1 or K2 to include or usethe angle threshold is a first angle threshold, and wherein the controlcircuit configured to generate the response indicative of theenvironmental condition of the instrument is configured to: in responseto the measured reference impedance angle being greater than the firstangle threshold, reduce the delivery of the therapeutic signal andgenerate a notification signal.

Aspect K4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects K1 through K3 to include oruse the error notification indicating a presence of a conductive foreignbody in the biological tissue.

Aspect K5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects K1 through K4 to include oruse the angle threshold being a first angle threshold, and wherein thecontrol circuit configured to generate the response indicative of theenvironmental condition of the instrument is configured to: in responseto the measured reference impedance angle being greater than a firstangle and less than a second angle, reduce a power level of thetherapeutic signal.

Aspect K6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects K1 through K5 to include oruse the angle threshold being a first angle threshold, and wherein thecontrol circuit is configured to: in response to the measured referenceimpedance angle being less than the first angle threshold, reduce thedelivery of the therapeutic signal.

Aspect K7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects K1 through K6 to include oruse the error notification indicating an open circuit.

Aspect K8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects K1 through K7 to include oruse a timer to measure an elapsed therapy time, wherein the controlcircuit is configured to: compare the elapsed therapy time to a timeconstant; and in response to the elapsed therapy time exceeding the timeconstant, the measurement circuit is configured to measure the referenceimpedance angle of the biological tissue.

L. Correction to Measured Tissue Resistance to Account for ElectrodeTemperature

Aspect L1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a method ofdelivering electrical energy to an electrosurgical device, the methodcomprising: delivering an electrotherapeutic signal to biological tissueto the electrosurgical device; measuring an impedance of the biologicaltissue; measuring an electrosurgical device sealing parameter; anddetermining an adjusted impedance based on a relationship between theelectrosurgical device sealing parameter and the measured impedance.

Aspect L2 can include or use or can optionally be combined with at leastsome features of Aspect L1 to include or use the electrosurgical devicesealing parameter including a temperature.

Aspect L3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects L1 or L2 to include or usethe electrosurgical device including jaws, and wherein the temperatureis a temperature of the jaws.

Aspect L4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects L1 through L3 to include oruse wherein determining the adjusted impedance based on the relationshipbetween the electrosurgical device sealing parameter and the measuredimpedance includes: comparing the electrosurgical device sealingparameter and the measured impedance to a stored data set; anddetermining the adjusted impedance based on the comparison.

Aspect L5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects L1 through L4 to include oruse determining a vessel size using the determined adjusted impedance.

Aspect L6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects L1 through L5 to include oruse determining at least one electrical parameter of an electrosurgicalsignal for delivery to the biological tissue.

Aspect L7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects L1 through L6 to include oruse the electrosurgical device sealing parameter including an elapsedtime after delivery of the electrotherapeutic signal.

M. Dwell Time Between Pulses

Aspect M1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a surgical systemcomprising: a control circuit; and an output circuit coupled to thecontrol circuit and configured to deliver energy to an output terminalfor delivery to a patient, the output terminal configured to couple toan electrosurgical device having two jaws with corresponding electrodes,wherein the control circuit is configured to: deliver first and secondelectrosurgical energy pulses to biological tissue in electricalcommunication with two electrodes of the surgical device, wherein thefirst and second electrosurgical energy pulses are separated from oneanother by a dwell time; and determine the dwell time following thefirst electrosurgical energy pulse.

Aspect M2 can include or use or can optionally be combined with at leastsome features of Aspect M1 to include or use the control circuitconfigured to determine the dwell time following the firstelectrosurgical energy pulse being configured to: determine an amount ofenergy delivered to the jaws; and determine the dwell time following thefirst electrosurgical energy pulse based on the determined amount ofenergy.

Aspect M3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects M1 or M2 to include or usethe control circuit configured to determine the dwell time following thefirst electrosurgical energy pulse based on the determined amount ofenergy is configured to: compare the determined amount of energy to astored data set; and determine the dwell time based on the comparison.

Aspect M4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects M1 through M3 to include oruse the control circuit configured to determine the dwell time followingthe first electrosurgical energy pulse being configured to: initiate atimer upon delivery of one of the electrosurgical energy pulses;determine that the biological tissue has boiled and stop the timer;compare the timer to one or more values; and determine the dwell timebased on the comparison.

Aspect M5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects M1 through M4 to include oruse the control circuit configured to determine the dwell time followingthe first electrosurgical energy pulse being configured to: determine anamount of energy delivered to the jaws; determine an electricalcharacteristic of the tissue; and determine the dwell time following thefirst electrosurgical energy pulse based on the determined amount ofenergy and the determined electrical characteristic.

Aspect M6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects M1 through M5 to include oruse the determined electrical characteristic being impedance.

Aspect M7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects M1 through M6 to include oruse the determined electrical characteristic being a phase angle.

Aspect M8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects M1 through M7 to include oruse the control circuit configured to determine the dwell time followingthe first electrosurgical energy pulse being configured to: determine anamount of current delivered during a previous electrosurgical energypulse; and determine the dwell time following the first electrosurgicalenergy pulse based on the determined amount of current.

Aspect M9 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects M1 through M8 to include oruse the control circuit configured to determine the dwell time followingthe first electrosurgical energy pulse being configured to: determine anamount of charge delivered during a previous electrosurgical energypulse; and determine the dwell time following the first electrosurgicalenergy pulse based on the determined amount of charge.

Aspect M10 can include or use or can optionally be combined with atleast some features of any one or more of Aspects M1 through M9 toinclude or use the control circuit configured to determine the dwelltime following the first electrosurgical energy pulse being configuredto: initiate a timer upon delivery of a current of one of theelectrosurgical energy pulses and stop the timer after the current isdelivered; compare the timer to one or more values; and determine thedwell time based on the comparison.

N. Pulsing at the End of the Drying Cycle

Aspect N1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use an electrosurgicalsystem for providing an electrotherapeutic signal to a biologicaltissue, the electrosurgical system comprising: a forceps including:opposable jaw members configured to open and close; and wherein theopposable jaw members, when closed, are configured to clamp thebiological tissue therebetween in a manner that provides electricalcommunication between the opposable jaw members via the clampedbiological tissue; and a control circuit in communication with anelectrical-energy source, the electrical-energy source electricallycoupled to the electrodes and configured to generate the therapeuticsignal, the control circuit configured to: cause the electrical-energysource to provide the electrotherapeutic signal to the biological tissueduring an electrotherapeutic phase, the electrotherapeutic signalprovided according to an electrotherapeutic plan; and cause theelectrical-energy source to pulse the electrotherapeutic signal providedto the biological tissue during a sticking reduction phase that followsthe electrotherapeutic phase, the electrotherapeutic signal pulsedaccording to a sticking-reduction plan configured to permit fluid toreturn to the clamped biological tissue thereby reducing sticking of thebiological tissue to the forceps.

Aspect N2 can include or use or can optionally be combined with at leastsome features of Aspect N1 to include or use a measurement circuit inelectrical communication with the opposable jaw members when theelectrical-energy source is electrically coupled to the forceps, themeasurement circuit configured to measure an electrical parameter of theclamped biological tissue including a reference impedance of thebiological tissue, wherein the control circuit is further configured to:determine a therapy time duration based on the measured referenceimpedance; reduce the electrotherapeutic phase when after determinedtherapy time duration has expired; and commence the sticking-reductionphase after the therapy time duration has expired.

Aspect N3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects N1 or N2 to include or usethe reference impedance being measured during an interrogation phase.

Aspect N4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects N1 through N3 to include oruse the reference impedance being measured during the electrotherapeuticphase.

Aspect N5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects N1 through N4 to include oruse the sticking-reduction plan has alternating electrical-power minimaand maxima, each of the electrical-power minima are below apredetermined threshold.

Aspect N6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects N1 through N5 to include oruse wherein each of the electrical-power minima of thesticking-reduction plan is maintained for a first predetermined timeduration.

Aspect N7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects N1 through N6 to include oruse the first predetermined time duration being greater than 10milli-seconds.

Aspect N8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects N1 through N7 to include oruse each of the electrical-power maxima of the sticking-reduction planis maintained for a second predetermined time duration.

Aspect N9 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects N1 through N8 to include oruse the second predetermined time duration being greater than 50milli-seconds.

Aspect N10 can include or use or can optionally be combined with atleast some features of any one or more of Aspects N1 through N9 toinclude or use the sticking-reduction plan being reduced after a thirdpredetermined time duration.

Aspect N11 can include or use or can optionally be combined with atleast some features of any one or more of Aspects N1 through N10 toinclude or use the third predetermined time duration is greater than 200milli-seconds.

Aspect N12 can include or use or can optionally be combined with atleast some features of any one or more of Aspects N1 through N11 toinclude or use the control circuit configured to pulse theelectrotherapeutic signal being configured to pulse theelectrotherapeutic signal according to a power-controlled plan.

Aspect N13 can include or use or can optionally be combined with atleast some features of any one or more of Aspects N1 through N12 toinclude or use the control circuit configured to pulse theelectrotherapeutic signal is configured to pulse the electrotherapeuticsignal according to a voltage-controlled plan.

Aspect N14 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use an electrosurgicalgenerator for providing an electrotherapeutic signal to a biologicaltissue in electrical communication with an electrosurgical instrument,the electrosurgical generator including: an electrical connectorconfigured to electrically couple the electrosurgical instrument to theelectrosurgical generator so as to provide electrical communicationbetween the electrosurgical generator and the biological tissue; anelectrical-energy source coupled to the electrical connector andconfigured to generate the electrotherapeutic signal; and a controlcircuit configured to: cause the electrical-energy source to provide theelectrotherapeutic signal to the biological tissue during anelectrotherapeutic phase, the electrotherapeutic signal providedaccording to an electrotherapeutic plan; and cause the electrical-energysource to pulse the electrotherapeutic signal provided to the biologicaltissue during a sticking reduction phase that follows theelectrotherapeutic phase, the electrotherapeutic signal pulsed accordingto a sticking-reduction plan configured to permit fluid to return to thebiological tissue thereby reducing sticking of the biological tissue tothe electrosurgical instrument.

Aspect N15 can include or use or can optionally be combined with atleast some features of Aspect N14 to include or use a measurementcircuit electrically coupled to the electrical connector and configuredto measure an electrical parameter of the biological tissue including areference impedance of the biological tissue, wherein the controlcircuit is further configured to: determine a therapy time durationbased on the measured reference impedance; reduce the electrotherapeuticphase when after determined therapy time duration has expired; andcommence the sticking-reduction phase after the therapy time durationhas expired.

Aspect N16 can include or use or can optionally be combined with atleast some features of any one or more of Aspects N14 or N15 to includeor use the sticking-reduction plan has alternating electrical-powerminima and maxima, and wherein each of the electrical-power minima ofthe sticking-reduction plan is maintained for a first predetermined timeduration greater than 50 milli-seconds.

Aspect N17 can include or use or can optionally be combined with atleast some features of any one or more of Aspects N14 through N16 toinclude or use wherein each of the electrical-power maxima of thesticking-reduction plan is maintained for a second predetermined timeduration greater than 50 milli-seconds.

Aspect N18 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a method fordelivering an electrotherapeutic signal to a biological tissue inelectrical communication with an electrosurgical instrument, theelectrosurgical instrument including a forceps having opposable jawmembers, the method including: providing, via an electrical-energysource, the electrotherapeutic signal to the biological tissue during anelectrotherapeutic phase, the electrotherapeutic signal providedaccording to an electrotherapeutic plan; and pulsing, via theelectrical-energy source, the electrotherapeutic signal provided to thebiological tissue during a sticking reduction phase that follows theelectrotherapeutic phase, the electrotherapeutic signal pulsed accordingto a sticking-reduction plan configured to permit fluid to return to thebiological tissue thereby reducing sticking of the biological tissue tothe electrosurgical instrument; releasing the biological tissue from theopposable jaw members of the forceps, after the pulsing reduction phase.

Aspect N19 can include or use or can optionally be combined with atleast some features of Aspect N18 to include or use measuring, via ameasurement circuit, a reference impedance of the biological tissue;determining a therapy time duration based on the measured referenceimpedance; reducing the electrotherapeutic phase when after determinedtherapy time duration has expired; and commencing the sticking-reductionphase after the therapy time duration has expired.

O. Terminating a Pulse Based Upon Measurements Taken Within the Pulse

Aspect O1 can include or use subject matter (e.g., a system, apparatus,method, article, or the like) that can include or use a method fordelivering an electrotherapeutic signal to biological tissue inelectrical communication with an electrosurgical instrument, the methodincluding: measuring a reference impedance of the biological tissueafter a time interval following commencement of a therapeutic phase;determining a termination criterion for the therapeutic phase based onthe measured reference impedance following commencement of thetherapeutic phase; delivering the electrotherapeutic signal to thebiological tissue during the therapeutic phase, the deliveredelectrotherapeutic signal controlled according to an electrotherapeuticplan; and terminating the therapeutic phase in response to thetermination criterion being met.

Aspect O2 can include or use or can optionally be combined with at leastsome features of Aspect O1 to include or use the termination criterionbeing a temporal criterion.

Aspect O3 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects O1 or O2 to include or usethe termination criterion being an impedance criterion.

Aspect O4 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects O1 through O3 to include oruse wherein determining a termination criterion for the therapeuticphase based on the measured reference impedance following commencementof the therapeutic phase includes: selecting between a temporalcriterion and an impedance criterion based on the measured referenceimpedance.

Aspect O5 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects O1 through O4 to include oruse the delivered electrotherapeutic signal being controlled accordingto a power-controlled therapeutic plan.

Aspect O6 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects O1 through O5 to include oruse the delivered electrotherapeutic signal being controlled accordingto a voltage-controlled therapeutic plan.

Aspect O7 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects O1 through O6 to include oruse the therapeutic phase being a desiccation phase.

Aspect O8 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects O1 through O7 to include oruse wherein determining a termination criterion for theelectrotherapeutic phase based on the measured reference impedanceincludes: comparing the measured reference impedance to a thresholdimpedance value, wherein the threshold impedance value is an absoluteimpedance value.

Aspect O9 can include or use or can optionally be combined with at leastsome features of any one or more of Aspects O1 through O8 to include oruse wherein determining a termination criterion for theelectrotherapeutic phase based on the measured reference impedanceincludes: comparing the measured reference impedance to a thresholdimpedance value, wherein the threshold impedance value is a deltaimpedance value.

Aspect O10 can include or use or can optionally be combined with atleast some features of any one or more of Aspects O1 through O9 toinclude or use the termination criterion being a first terminationcriterion, wherein the electrotherapeutic signal is a firstelectrotherapeutic signal, wherein the therapeutic phase is adesiccation phase, and wherein the reference impedance is a firstreference impedance, the method comprising: measuring a second referenceimpedance of the biological tissue following termination of thedesiccation phase; determining a second termination criterion for avessel welding phase based on the measured second reference impedanceprior to commencement of the vessel welding phase; delivering a secondelectrotherapeutic signal to the biological tissue during the vesselwelding phase; and terminating the vessel welding phase in response tothe second termination criterion being met.

Aspect O11 can include or use or can optionally be combined with atleast some features of any one or more of Aspects O1 through O10 toinclude or use the second termination criterion being a temporalcriterion.

Aspect O12 can include or use or can optionally be combined with atleast some features of any one or more of Aspects O1 through O11 toinclude or use the second termination criterion being an impedancecriterion.

Aspect O13 can include or use or can optionally be combined with atleast some features of any one or more of Aspects O1 through O12 toinclude or use wherein determining a second termination criterion for avessel welding phase based on the measured second reference impedanceprior to commencement of the vessel welding phase includes: selectingbetween a temporal criterion and an impedance criterion based on themeasured reference impedance.

Notes

Each of the non-limiting aspects or examples described herein may standon its own, or may be combined in various permutations or combinationswith one or more of the other examples.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific examples in which the inventionmay be practiced. These examples are also referred to herein as“examples.” Such examples may include elements in addition to thoseshown or described. However, the present inventors also contemplateexamples in which only those elements shown or described are provided.Moreover, the present inventors also contemplate examples using anycombination or permutation of those elements shown or described (or oneor more aspects thereof), either with respect to a particular example(or one or more aspects thereof), or with respect to other examples (orone or more aspects thereof) shown or described herein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

Method examples described herein may be machine or computer-implementedat least in part. Some examples may include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods may include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code may include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code may be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media may include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact discs and digital video discs), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherexamples may be used, such as by one of ordinary skill in the art uponreviewing the above description. The Abstract is provided to comply with37 C.F.R. §1.72(b), to allow the reader to quickly ascertain the natureof the technical disclosure. It is submitted with the understanding thatit will not be used to interpret or limit the scope or meaning of theclaims. Also, in the above Detailed Description, various features may begrouped together to streamline the disclosure. This should not beinterpreted as intending that an unclaimed disclosed feature isessential to any claim. Rather, inventive subject matter may lie in lessthan all features of a particular disclosed example. Thus, the followingclaims are hereby incorporated into the Detailed Description as examplesor examples, with each claim standing on its own as a separate example,and it is contemplated that such examples may be combined with eachother in various combinations or permutations. The scope of theinvention should be determined with reference to the appended claims,along with the full scope of equivalents to which such claims areentitled.

1. An electrosurgical generator configured to generate and provide atherapeutic signal to biological tissue in electrical communication witha surgical instrument, the surgical generator comprising: a measurementcircuit coupled to a control circuit and configured to measure areference impedance angle of the biological tissue during aninterrogation phase; and the control circuit in communication with anelectrical-energy source, the electrical-energy source electricallycoupled to the instrument and configured to generate the therapeuticsignal, the control circuit configured to: control delivery of thetherapeutic signal provided to the biological tissue; compare themeasured reference impedance angle with an angle threshold; and generatea response indicative of an environmental condition of the instrumentbased on the comparison of the measured reference impedance angle withthe angle threshold.
 2. The electrosurgical generator of claim 1,wherein the measured reference impedance angle is substantially equal toan angular difference between a voltage across and current conducted bythe biological tissue as measured by the measurement circuit.
 3. Theelectrosurgical generator of claim 2, wherein the angle threshold is afirst angle threshold, and wherein the control circuit configured togenerate the response indicative of the environmental condition of theinstrument is configured to: in response to the measured referenceimpedance angle being greater than the first angle threshold, reduce thedelivery of the therapeutic signal and generate an error notificationsignal.
 4. The electrosurgical generator of claim 3, wherein the errornotification indicates a presence of a conductive foreign body in thebiological tissue.
 5. The electrosurgical generator of claim 2, whereinthe angle threshold is a first angle threshold, and wherein the controlcircuit configured to generate the response indicative of theenvironmental condition of the instrument is configured to: in responseto the measured reference impedance angle being greater than a firstangle and less than a second angle, reduce a power level of thetherapeutic signal.
 6. The electrosurgical generator of claim 2, whereinthe angle threshold is a first angle threshold, and wherein the controlcircuit is configured to: in response to the measured referenceimpedance angle being less than the first angle threshold, reduce thedelivery of the therapeutic signal.
 7. The electrosurgical generator ofclaim 6, wherein the error notification indicates an open circuit. 8.The electrosurgical generator of claim 1, comprising: a timer to measurean elapsed therapy time, wherein the control circuit is configured to:compare the elapsed therapy time to a time constant; and in response tothe elapsed therapy time exceeding the time constant, the measurementcircuit is configured to measure the reference impedance angle of thebiological tissue.